fix(lint): apply QA-found gaps in agent instruction files

- python-coder.md: ruff check src/ tests/ → ruff check .
- speckit.test.md: add frontend npm run lint
- speckit.plan.md: ruff check . + frontend lint
- speckit.tasks.md: ruff check . + frontend lint
- fullstack-coder.md: move npm run lint to frontend block

.opencode/command/speckit.test.md

@@ -83,6 +83,7 @@ Run the smallest truthful verifier set for the touched scope:
 # Backend
 cd backend && source .venv/bin/activate && python -m pytest -v
 python -m ruff check backend/src/ backend/tests/
+cd frontend && npm run lint
 
 # Frontend
 cd frontend && npm run test