bmersereau wants a misconfigured backend to fail loudly, not limp along

Right now, if the fork's backend starts up without the connection details for Supabase - the hosted database and login service the app runs on - it quietly builds a broken connection anyway and only trips up later, with errors that are hard to trace back to the real cause. bmersereau's change flips that: if the credentials are absent, the service stops immediately at startup and says exactly what's missing.

The work also cleared out an unused piece of old code carrying the same silent-failure habit, and added the backend's first automated tests to lock the new behavior in place. It's the kind of guardrail that turns a whole category of setup mistakes from a late-night debugging session into an obvious error message. Worth noting: the tests passed and the build was clean, but the proposal was closed in late June without being merged, so this hasn't actually landed.