feat: Migrationen für campaigns-Tabellen (PostgreSQL) und email_events (ClickHouse)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

migrations/ch/2026-04-17_email_events.sql

@@ -0,0 +1,11 @@
+CREATE TABLE IF NOT EXISTS newsletter.email_events (
+  event_type    LowCardinality(String),
+  tenant_id     String,
+  campaign_id   UUID,
+  recipient_hash String,
+  timestamp     DateTime64(3, 'UTC'),
+  metadata      Map(String, String)
+)
+ENGINE = MergeTree()
+PARTITION BY toYYYYMM(timestamp)
+ORDER BY (tenant_id, campaign_id, event_type, timestamp);