Fix linting errors across backend and frontend

Backend: auto-fix and format all ruff issues, manually fix B904/B023/
SIM117/B007/E741/F841 errors, suppress B008 (FastAPI Depends) and F821
(SQLAlchemy forward refs) in config. Frontend: allow constant exports,
disable React compiler-specific rules (set-state-in-effect,
preserve-manual-memoization).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/pyproject.toml

@@ -47,8 +47,12 @@ select = [
 ]
 ignore = [
     "E501",   # line too long (handled by formatter)
+    "B008",   # Depends() in defaults — standard FastAPI pattern
 ]
 
+[tool.ruff.lint.per-file-ignores]
+"src/app/models/*.py" = ["F821"]  # forward refs in SQLAlchemy relationships
+
 [tool.ruff.lint.isort]
 known-first-party = ["app"]