v0.5.5-beta: SQLite Volume Permission Hotfix

[DeepZone]

Motivation

• Prevent sqlite3.OperationalError: attempt to write a readonly database when a root-owned Docker volume is mounted at /app/data while the container runs as the non-root runtime user routeforge.

Description

• Add backend/docker-entrypoint.sh which creates /app/data, chown-es it to routeforge:routeforge and then drops to the runtime user via gosu routeforge "$@".
• Ensure the backend image provides gosu, prepares /app and /app/data, and installs the entrypoint script as an executable (entrypoint execution is done in the image at build time).
• Bump user-facing and package version strings to v0.5.5-beta / 0.5.5 across backend and frontend surfaces and tests, and update RELEASE_NOTES.md with the hotfix entry.
• Add troubleshooting docs docs/operations/troubleshooting.md and a short README note explaining the SQLite permission behavior and containing the workaround using docker compose run --rm --user root backend sh -c "mkdir -p /app/data && chown -R routeforge:routeforge /app/data && chmod -R u+rwX /app/data" for older releases.

Testing

• Ran backend unit tests with cd backend && pytest -q, all tests passed (77 passed).
• Built frontend with cd frontend && npm run build, build completed successfully (vite build produced dist/ output).
• Attempted Docker runtime verification (docker compose build / up and HTTP status check) but docker is not available in this environment, so runtime smoke test could not be executed here.

---

Codex Task