refactor: consolidate commit hooks, add lint gate, trim CLAUDE.md (#397)

* refactor: consolidate commit hooks, add lint gate, trim CLAUDE.md

- Consolidate 3 slow pre-commit hooks (show-diff-impact, check-commit,
  check-dead-exports) into single pre-commit.sh + pre-commit-checks.js
  that runs one Node.js process for all codegraph checks
- Add lint-staged.sh hook that blocks commits with lint errors
- Delete remind-codegraph.sh (ignored by Claude), warn-signature-changes.sh
  and check-cycles.sh (redundant with check-commit.sh consolidation)
- Remove dead codegraph-checked.log references from post-git-ops.sh
- Trim CLAUDE.md: replace dogfooding command list with hooks table,
  remove Working Principles section (now enforced by hooks)
- Update examples, guides, and BACKLOG.md with new hook-optimized
  brief command proposal (ID 83)

Impact: 1 functions changed, 0 affected

* fix: address Greptile review — bump timeout, fix JSDoc order, document fail-open

* fix: scan .ts/.tsx in scanDynamic and correct pre-commit timeout in docs

- scanDynamic() now processes .ts and .tsx files in addition to .js,
  preventing TypeScript dynamic imports from being invisible to the
  public API allowlist check
- Update ai-agent-guide pre-commit.sh timeout example from 30 to 60,
  matching the actual value in settings.json

* fix: scan .ts/.tsx in scanDynamic in example copy

* fix: use array for file list in lint-staged.sh to handle spaces in paths

Author: carlos-alm