feat(v5.2.0): finalize Infrastructure & Polish (tests isolation, xdist, lint, CI)

tests/conftest.py: mutate the settings singleton (instead of rebinding) so DB + backup dir are isolated per test -> pytest-xdist safe.
Real backup tests (snapshot/prune/admin API) and OAuth mock tests (Gitea/GitHub/link) replace the previous skips.
init_db() now also creates webhook_subscriptions (full schema without the FastAPI lifespan).
ruff check is clean; .eslintrc.json migrated to eslint.config.mjs (flat config).
CI: lint job (ruff + eslint), parallel tests (-n auto), run on every branch push.
VERSION 5.11.1.

app/routers/collaboration.py

@@ -50,7 +50,7 @@ def _serialize(rows):
 @router.get("/pages/{page_id}/comments")
 async def list_comments(request: Request, page_id: int):
     """List page-level and inline comments for a FlowDeck page."""
-    user = _current_user(request)
+    _current_user(request)
     with get_conn() as conn:
         page = conn.execute("SELECT id, title FROM pages WHERE id=?", (page_id,)).fetchone()
         if not page: