CI: add pre-commit config

## Background
Development.md references a `.pre-commit-config.yaml` that doesn't exist.

## Why it matters
Local quality gate parity with CI.

## Acceptance criteria
- [ ] Create `.pre-commit-config.yaml` (ruff, mypy, bandit).
- [ ] Document usage.

## Where to look
- `Development.md`, `.pre-commit-config.yaml` (new)

## How to claim
Comment `/claim` on this issue.