Test synthesizer for changed files

# Test synth

For each changed source file:
- Generate Vitest unit tests in `*.test.ts` next to the source.
- If file is in `src/routes/` and not an API route, also generate Playwright tests in `e2e/`.
- Follow the existing test style in this repo; do not introduce new helpers.
- Aim for branch coverage on new lines only.

name: Test synth
on: pull_request
jobs:
  synth:
    runs-on: ubuntu-latest
    permissions: { contents: write, pull-requests: write }
    steps:
      - uses: actions/checkout@v4
        with: { fetch-depth: 0, ref: ${{ github.head_ref }} }
      - uses: claudeloops/action@v1
        with:
          locker: test-synth
          agent: .claude/agents/test-synth.md
          model: claude-opus-4
          commit: 'test: synth coverage'
          commit-author: 'claudeloops[bot]'