Adds GET /api/projects/[id]/codebases that inspects the project's
Gitea repo:
- apps/* present → one codebase per subdir (Turborepo)
- else → single codebase rooted at the repo root
- no repo → empty list with reason="no_repo"
Product tab now fetches this list, picks the first as the default
selection, and surfaces explicit loading / error / empty states
(previously it hung on "Loading…" when apps/web 404'd in single-
repo projects).
Made-with: Cursor
