Implement a check for GitHub OAuth credentials to conditionally render
the GitHub sign-in button. This ensures the UI accurately reflects
available authentication methods based on environment configuration.
- Add `isGithubAuthEnabled` utility to verify server-side credentials
- Propagate GitHub auth status through context providers to the UI
- Conditionally display the GitHub sign-in button in the sign-in page
- Update documentation and examples to use hex encoding for `AUTH_SECRET`
- Add unit tests for the new GitHub authentication configuration logic
- Introduce `USE_ANONYMOUS_AUTH_SESSIONS` to make guest access an opt-in feature.
- Transition root-level pages into `(app)` and `(public)` route groups for improved access control.
- Adopt Figtree as the primary typeface and implement a pre-render theme initialization script.
- Decouple audiobook chapter processing into a standalone API route and harden resource ownership logic.
- Replace the legacy footer with a unified layout and add skeleton loading states for document lists.
- Update environment documentation and test suites to align with the revised routing and auth flows.
BREAKING CHANGE: The audiobook generation API has been restructured, moving specific chapter logic to `/api/audiobook/chapter`.
