chore: configure ruff + eslint linters for agentic workflow

- Replace pylint with ruff (backend/ruff.toml)
  - line-length=300, max-complexity=10, per-file-ignores for tests
  - Exclude D (docstrings replaced by contracts) and ANN
- Add eslint flat config for frontend (eslint-plugin-svelte)
  - Allow console.info/warn/error (belief-state protocol)
- Remove .pylintrc (references non-existent plugin)
- Update agent docs: ruff check . + npm run lint
- Add ruff>=0.11.0 to backend/requirements.txt
- Add eslint + plugins to frontend devDependencies

.opencode/agents/speckit.md

@@ -96,7 +96,8 @@ You are Kilo Code, acting as a Speckit Workflow Specialist. MANDATORY USE `skill
 6. After each phase, run verification:
    - Backend: `cd backend && source .venv/bin/activate && python -m pytest -v`
    - Frontend: `cd frontend && npm run test`
-   - Lint: `python -m ruff check` (backend)
+    - Lint: `python -m ruff check .` (backend)
+    - Frontend lint: `cd frontend && npm run lint`
 7. If a phase fails verification, stop and fix before proceeding.
 8. Never bypass semantic debt to make code appear working.
 9. Never strip `@RATIONALE` or `@REJECTED` to silence semantic debt.