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/command/speckit.implement.md

@@ -42,7 +42,8 @@ You **MUST** consider the user input before proceeding (if not empty).
 - Active feature docs always live under `specs/<feature>/...` and are discovered via the `.specify/scripts/bash/*` helpers.
 - Default verification stack:
   - Backend: `cd backend && source .venv/bin/activate && python -m pytest -v`
-  - Backend lint: `python -m ruff check backend/src/ backend/tests/`
+  - Backend lint: `cd backend && python -m ruff check .`
+  - Frontend lint: `cd frontend && npm run lint`
   - Frontend: `cd frontend && npm run test`
   - Frontend build: `cd frontend && npm run build`
 - Do not fall back to Rust `cargo`/`src/server/` conventions — this is a Python/Svelte project.