Add Docker packaging and migrate from better-sqlite3 to libsql

Docker self-hosting support:
- Dockerfile (multi-stage Alpine build with tini init)
- docker-compose.yml with named volume for SQLite persistence
- /api/health endpoint for container health checks
- Auto-migration on startup via drizzle-orm/libsql/migrator
- Graceful shutdown (SIGTERM stops scheduler, closes DB)
- Next.js standalone output mode for minimal image size

Database driver migration (better-sqlite3 → @libsql/client):
- Eliminates native C++ compilation, enabling Alpine Docker images
- All DB queries converted from sync to async across services and routes
- DATABASE_URL now uses libsql file: prefix format
- drizzle.config.ts dialect changed to turso for libsql support
- Initial migration files generated in drizzle/

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

drizzle.config.ts

@@ -1,10 +1,10 @@
 import { defineConfig } from "drizzle-kit";
 
 export default defineConfig({
-  dialect: "sqlite",
+  dialect: "turso",
   schema: "./lib/db/schema.ts",
   out: "./drizzle",
   dbCredentials: {
-    url: process.env.DATABASE_URL ?? "sqlite.db",
+    url: process.env.DATABASE_URL ?? "file:sqlite.db",
   },
 });