chore: add pre-commit hooks with husky and lint-staged

[PaulGrimshaw]

Context

There are no pre-commit hooks. Contributors can push code that fails lint/format checks, causing noisy CI failures.

Change required

pnpm add -Dw husky lint-staged
pnpm exec husky init

.husky/pre-commit:

pnpm exec lint-staged

Root package.json:

"lint-staged": {
  "**/*.ts": ["eslint --fix", "prettier --write"]
}

This catches formatting and lint issues locally before they hit CI.