Initialize backend foundation for auth and data services

[ramonverse]

Establish a backend worker that can handle authentication, database access, and core app APIs. This lays the groundwork for server-side features like user sessions, course data, and conversation storage behind a single Hono app.

• Added a Hono-based backend entrypoint with /api/auth/* routing, /health, shared request context, and centralized error handling.
• Wired Better Auth to Drizzle/Postgres with email/password login, Google sign-in, Turnstile protection, custom password reset email content, and signup hooks.
• Created database connection helpers that support either HYPERDRIVE or DATABASE_URL, plus a Drizzle config and backend package scripts for dev/build/deploy/types.
• Added shared backend utilities for HTTP errors, safe JSON parsing, R2 audio upload/download, GitHub star lookup, and unit content parsing.
• Introduced backend service modules for chats, courses, feedback, lessons, preferences, profile, progress, and prompts to support server-managed app data.

[cord-app-staging]

Started in Cord: https://app.staging-runcord.xyz/f925bf62-6451-4e17-bab7-781360723f68/c83fd8b6-28d8-4c33-8469-742daa3729d1