Switch from Node.js + pnpm to Bun runtime and package manager

Replace @libsql/client with bun:sqlite for zero-dependency SQLite access,
swap drizzle-orm/libsql adapter for drizzle-orm/bun-sqlite, and rewrite
Dockerfile to use oven/bun:1-alpine. The raw Database instance is no longer
exported via Proxy (native C++ methods lose `this` binding through
Reflect.get); instead, a closeDatabase() helper handles graceful shutdown
and the health check uses Drizzle's db.run() directly.

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

.env.example

@@ -12,7 +12,7 @@ TMDB_API_READ_ACCESS_TOKEN=
 
 # ─── Auth (required) ───────────────────────────────────────────────────────
 # Random secret for session encryption (min 32 chars)
-# Generate one with `npx @better-auth/cli secret` or `openssl rand -base64 32`
+# Generate one with `bunx @better-auth/cli secret` or `openssl rand -base64 32`
 BETTER_AUTH_SECRET=
 # Public URL of your instance, especially important if reverse proxy is used
 BETTER_AUTH_URL=http://localhost:3000