feat(phase-0): stability hardening — search path fix, auto-migrations, graceful shutdown, health endpoint

- Remove SET search_path from db.py and migration SQL (Supabase uses public schema)
- Add migrate.py with tracking table for forward-only SQL migrations
- Add entrypoint.sh: waits for DB, runs migrations, then starts app
- Copy 01-schema.sql + zz-seed.sql to worker/src/migrations/
- Add health.py: /health endpoint (200/503) with DB connectivity + scheduler staleness checks
  - /stats endpoint with keyword/ad/notification counts
- Rewrite main.py shutdown sequence: signal handler, 5s grace for scheduler, ordered cleanup
- Update Dockerfile: HEALTHCHECK directive, entrypoint, COPY migrations
- Update docker-compose.yml: stop_grace_period=15s, healthcheck config, env vars
- Add aiohttp>=3.9 to requirements.txt for health server

worker/src/entrypoint.sh

@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# ────────────────────────────────────────────────
+# Entrypoint: Run migrations, then start the app.
+# ────────────────────────────────────────────────
+
+echo "[entrypoint] Waiting for database to be ready..."
+
+# Wait for PostgreSQL to accept connections (max 30s retries)
+for i in $(seq 1 30); do
+    if python -c "import asyncpg,os; asyncio.get_event_loop().run_until_complete(
+        asyncpg.connect(
+            host=os.getenv('POSTGRES_HOST','db'),
+            port=int(os.getenv('POSTGRES_PORT','5432')),
+            user=os.getenv('POSTGRES_USER','postgres'),
+            password=os.getenv('POSTGRES_PASSWORD'),
+            database=os.getenv('POSTGRES_DB','postgres'),
+        )
+    )" 2>/dev/null; then
+        echo "[entrypoint] Database is ready."
+        break
+    fi
+    if [ "$i" -eq 30 ]; then
+        echo "[entrypoint] ERROR: Could not connect to database after 30 attempts." >&2
+        exit 1
+    fi
+    sleep 1
+done
+
+# ── Run migrations ──────────────────────────────
+echo "[entrypoint] Running database migrations..."
+python /app/migrate.py || {
+    echo "[entrypoint] ERROR: Migration failed — aborting startup." >&2
+    exit 1
+}
+echo "[entrypoint] Migrations complete."
+
+# ── Start the application ───────────────────────
+exec "$@"