**feat(compose):** add separate deploy and dev Docker Compose files

- Introduced `compose.yml` for deployment, pulling the image from the registry
- Added `compose.dev.yml` for local development, building the image from source
- Updated `README.md` and `.claude/CLAUDE.md` with instructions for both configurations
- Introduced `DB_PATH` environment variable to customize SQLite database file location
- Updated `main.go` to use `DB_PATH` with a default fallback (`./diun.db`)

compose.dev.yml

@@ -0,0 +1,8 @@
+services:
+  app:
+    build: .
+    ports:
+      - "8080:8080"
+    environment:
+      - WEBHOOK_SECRET=${WEBHOOK_SECRET:-}
+    restart: unless-stopped