[M4] Event-to-Narration Synchronizer

[cursor]

Milestone 4 — Playwright Test Video Integration | Priority: High | COMPLETED in PR #27

Align narration audio timing to Playwright browser events extracted from traces. Analogous to tape_sync.py for VHS.

• Match configured anchors (action+selector → narration keyword)
• Auto-match: extract keywords from selectors/URLs, cross-reference with Whisper words
• Compute piece-wise speed factors between anchor points
• Output sync_map.json
• CLI: docgen sync-playwright [--segment 03] [--dry-run]

Implemented in src/docgen/playwright_sync.py. See issues/playwright-test-integration/03-event-narration-sync.md.