Update README: Add geofencing architecture and update tech stack

Documentation updates:
- Add geofencing feature description with capabilities
- Update database architecture ER diagram with Geofence, GeofenceEvent, and GeofenceStatus tables
- Add complete schema documentation for all geofence tables and indexes
- Update data flow diagram to show geofence monitoring pipeline
- Update component overview with Geofence Monitor
- Update Tech Stack versions: Next.js 16.0.7, React 19.2.1
- Add MQTT.js, Eclipse Mosquitto, Nodemailer, React Email to tech stack
- Update dual-database architecture description
- Add npm run db:init:geofence command documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

README.md

@@ -40,6 +40,12 @@ Eine moderne Location-Tracking Anwendung basierend auf Next.js 14 mit MQTT/OwnTr
 - 📊 **Dashboard** - Übersicht über Geräte, Statistiken und Datenbankstatus
 - ⏱️ **System Status** - Live-Uptime, Memory Usage, Runtime Info
 - 📱 **Device Management** - Geräte hinzufügen, bearbeiten, löschen
+- 🎯 **Geofencing** - Kreisförmige Geofences mit Enter/Exit-Benachrichtigungen:
+  - Geofences erstellen, bearbeiten und löschen
+  - Radius 50m bis 50km konfigurierbar
+  - Visualisierung auf der Karte mit Toggle-Button
+  - Event-Historie mit Enter/Exit-Ereignissen
+  - E-Mail und MQTT-Benachrichtigungen bei Grenzüberschreitung
 - 💾 **Datenbank-Wartung**:
   - 🧹 Cleanup alter Daten (7, 15, 30, 90 Tage)
   - ⚡ Datenbank-Optimierung (VACUUM)
@@ -51,17 +57,20 @@ Eine moderne Location-Tracking Anwendung basierend auf Next.js 14 mit MQTT/OwnTr
 
 ## 🛠 Tech Stack
 
-- **Framework:** Next.js 14 (App Router)
+- **Framework:** Next.js 16.0.7 (App Router)
+- **Runtime:** React 19.2.1
 - **Sprache:** TypeScript 5.9
 - **Styling:** Tailwind CSS v4
 - **Karten:** Leaflet 1.9.4 + React-Leaflet 5.0
 - **Authentifizierung:** NextAuth.js v5 (beta)
 - **Datenbank:** SQLite (better-sqlite3)
+- **MQTT:** MQTT.js v5 + Eclipse Mosquitto
+- **E-Mail:** Nodemailer + React Email
 - **Passwort-Hashing:** bcryptjs
 - **Datenquelle:** MQTT Broker + lokale SQLite-Cache
 
 ### Dual-Database Architektur
-- **database.sqlite** - User, Geräte (kritische Daten)
+- **database.sqlite** - User, Geräte, MQTT-Credentials, Geofences (kritische Daten)
 - **locations.sqlite** - Location-Tracking (hohe Schreibrate, isoliert)
 
 ---
@@ -91,7 +100,7 @@ npm run db:init
 ```
 
 Dies erstellt:
-- `data/database.sqlite` (User + Devices)
+- `data/database.sqlite` (User + Devices + MQTT + Geofences)
 - `data/locations.sqlite` (Location-Tracking)
 - Standard Admin-User: `admin` / `admin123`
 - Standard Devices (ID 10, 11)
@@ -128,6 +137,11 @@ npm run db:init:app
 npm run db:init:locations
 ```
 
+**Nur Geofence-Tabellen:**
+```bash
+npm run db:init:geofence
+```
+
 ### Datenbank zurücksetzen
 
 **Admin-User neu anlegen:**
@@ -207,6 +221,52 @@ created_at          TEXT DEFAULT (datetime('now'))
 updated_at          TEXT DEFAULT (datetime('now'))
 ```
 
+**Geofence Tabelle:**
+```sql
+id                  TEXT PRIMARY KEY
+name                TEXT NOT NULL
+description         TEXT
+shape_type          TEXT NOT NULL DEFAULT 'circle'      -- Only 'circle' for MVP
+center_latitude     REAL NOT NULL
+center_longitude    REAL NOT NULL
+radius_meters       INTEGER NOT NULL
+owner_id            TEXT NOT NULL                       -- FK zu User.id
+device_id           TEXT NOT NULL                       -- FK zu Device.id
+is_active           INTEGER DEFAULT 1                   -- 0 oder 1
+color               TEXT DEFAULT '#3b82f6'
+created_at          TEXT DEFAULT (datetime('now'))
+updated_at          TEXT DEFAULT (datetime('now'))
+```
+
+**GeofenceEvent Tabelle:**
+```sql
+id                      INTEGER PRIMARY KEY AUTOINCREMENT
+geofence_id             TEXT NOT NULL                   -- FK zu Geofence.id
+device_id               TEXT NOT NULL                   -- FK zu Device.id
+location_id             INTEGER NOT NULL
+event_type              TEXT NOT NULL                   -- 'enter' oder 'exit'
+latitude                REAL NOT NULL
+longitude               REAL NOT NULL
+distance_from_center    REAL
+notification_sent       INTEGER DEFAULT 0               -- 0=not sent, 1=sent, 2=failed
+notification_error      TEXT
+timestamp               TEXT NOT NULL
+created_at              TEXT DEFAULT (datetime('now'))
+```
+
+**GeofenceStatus Tabelle:**
+```sql
+id                  INTEGER PRIMARY KEY AUTOINCREMENT
+device_id           TEXT NOT NULL                       -- FK zu Device.id
+geofence_id         TEXT NOT NULL                       -- FK zu Geofence.id
+is_inside           INTEGER NOT NULL DEFAULT 0          -- 0 oder 1
+last_enter_time     TEXT
+last_exit_time      TEXT
+last_checked_at     TEXT
+created_at          TEXT DEFAULT (datetime('now'))
+updated_at          TEXT DEFAULT (datetime('now'))
+```
+
 **Indexes:**
 - `idx_user_username` ON User(username)
 - `idx_user_parent` ON User(parent_user_id)
@@ -215,6 +275,17 @@ updated_at          TEXT DEFAULT (datetime('now'))
 - `idx_mqtt_credentials_device` ON mqtt_credentials(device_id)
 - `idx_mqtt_credentials_username` ON mqtt_credentials(mqtt_username)
 - `idx_mqtt_acl_device` ON mqtt_acl_rules(device_id)
+- `idx_geofence_owner` ON Geofence(owner_id)
+- `idx_geofence_device` ON Geofence(device_id)
+- `idx_geofence_active` ON Geofence(is_active)
+- `idx_geofence_event_geofence` ON GeofenceEvent(geofence_id)
+- `idx_geofence_event_device` ON GeofenceEvent(device_id)
+- `idx_geofence_event_timestamp` ON GeofenceEvent(timestamp DESC)
+- `idx_geofence_event_notification` ON GeofenceEvent(notification_sent)
+- `idx_geofence_event_composite` ON GeofenceEvent(device_id, geofence_id, timestamp DESC)
+- `idx_geofence_status_device` ON GeofenceStatus(device_id)
+- `idx_geofence_status_geofence` ON GeofenceStatus(geofence_id)
+- `idx_geofence_status_inside` ON GeofenceStatus(is_inside)
 
 ---
 
@@ -328,6 +399,8 @@ flowchart TD
     B -->|Subscribe| C[📡 Next.js MQTT Subscriber]
 
     C -->|Store Locations| D[(🗄️ SQLite Cache<br/>locations.sqlite)]
+    C -->|Check Geofences| L[🎯 Geofence Monitor]
+    L -->|Store Events| K[(💼 SQLite DB<br/>database.sqlite)]
 
     E[🖥️ Browser Client] -->|GET /api/locations<br/>alle 5 Sek| F[📡 Next.js API Route]
 
@@ -335,10 +408,13 @@ flowchart TD
     F -->|JSON Response| E
 
     E -->|Render| G[🗺️ React Leaflet Map]
+    E -->|Render Geofences| M[🔵 Geofence Circles]
 
     H[👤 Admin User] -->|Login| I[🔐 NextAuth.js]
     I -->|Authenticated| J[📊 Admin Panel]
-    J -->|CRUD Operations| K[(💼 SQLite DB<br/>database.sqlite)]
+    J -->|CRUD Operations| K
+    J -->|Manage Geofences| K
+    K -->|Query Events| J
 
     style A fill:#4CAF50
     style B fill:#FF9800
@@ -348,6 +424,8 @@ flowchart TD
     style G fill:#8BC34A
     style I fill:#E91E63
     style K fill:#FFC107
+    style L fill:#9C27B0
+    style M fill:#3F51B5
 ```
 
 ### Komponenten-Übersicht
@@ -361,6 +439,7 @@ graph LR
 
     subgraph "Next.js Application"
         C[MQTT Subscriber]
+        I[Geofence Monitor]
         D[Frontend<br/>React/Leaflet]
         E[API Routes]
         F[Auth Layer<br/>NextAuth.js]
@@ -368,12 +447,14 @@ graph LR
 
     subgraph "Data Layer"
         G[locations.sqlite<br/>Tracking Data]
-        H[database.sqlite<br/>Users & Devices]
+        H[database.sqlite<br/>Users, Devices<br/>MQTT, Geofences]
     end
 
     A -->|MQTT| B
     B -->|Subscribe| C
-    C -->|Write| G
+    C -->|Write Locations| G
+    C -->|Trigger| I
+    I -->|Check & Store Events| H
 
     D -->|HTTP| E
     E -->|Read/Write| G
@@ -385,6 +466,7 @@ graph LR
     style A fill:#4CAF50,color:#fff
     style B fill:#FF9800,color:#fff
     style C fill:#2196F3,color:#fff
+    style I fill:#9C27B0,color:#fff
     style D fill:#00BCD4,color:#000
     style E fill:#00BCD4,color:#000
     style F fill:#E91E63,color:#fff
@@ -398,9 +480,15 @@ graph LR
 erDiagram
     USER ||--o{ USER : "parent_user_id"
     USER ||--o{ DEVICE : owns
+    USER ||--o{ GEOFENCE : owns
     DEVICE ||--o{ LOCATION : tracks
     DEVICE ||--o| MQTT_CREDENTIALS : has
     DEVICE ||--o{ MQTT_ACL_RULES : has
+    DEVICE ||--o{ GEOFENCE : monitors
+    GEOFENCE ||--o{ GEOFENCE_EVENT : triggers
+    GEOFENCE ||--o{ GEOFENCE_STATUS : tracks
+    DEVICE ||--o{ GEOFENCE_EVENT : generates
+    DEVICE ||--o{ GEOFENCE_STATUS : has
 
     USER {
         string id PK
@@ -450,6 +538,49 @@ erDiagram
         datetime updated_at
     }
 
+    GEOFENCE {
+        string id PK
+        string name
+        string description
+        string shape_type
+        float center_latitude
+        float center_longitude
+        int radius_meters
+        string owner_id FK
+        string device_id FK
+        boolean is_active
+        string color
+        datetime created_at
+        datetime updated_at
+    }
+
+    GEOFENCE_EVENT {
+        int id PK
+        string geofence_id FK
+        string device_id FK
+        int location_id
+        string event_type
+        float latitude
+        float longitude
+        float distance_from_center
+        int notification_sent
+        string notification_error
+        datetime timestamp
+        datetime created_at
+    }
+
+    GEOFENCE_STATUS {
+        int id PK
+        string device_id FK
+        string geofence_id FK
+        boolean is_inside
+        datetime last_enter_time
+        datetime last_exit_time
+        datetime last_checked_at
+        datetime created_at
+        datetime updated_at
+    }
+
     LOCATION {
         int id PK
         float latitude