fix: Suppression-Check nutzt SHA256-Hash statt Klartext-E-Mail (Finding 1)

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

migrations/pg/2026-04-17_suppression-list-hashed.sql

@@ -0,0 +1,13 @@
+-- Schritt 1: Hash-Spalte hinzufügen (additiv, kein Breaking Change)
+ALTER TABLE suppression_list ADD COLUMN IF NOT EXISTS email_hash TEXT;
+
+CREATE INDEX IF NOT EXISTS idx_suppression_list_email_hash ON suppression_list(email_hash);
+
+-- Schritt 2: Bestehende Einträge hashen (PostgreSQL-native SHA256)
+UPDATE suppression_list
+  SET email_hash = encode(sha256(lower(trim(email))::bytea), 'hex')
+  WHERE email_hash IS NULL;
+
+-- Schritt 3 (nach Validierung separat ausführen):
+-- ALTER TABLE suppression_list ALTER COLUMN email_hash SET NOT NULL;
+-- ALTER TABLE suppression_list DROP COLUMN email;