feat(prd-1): implement M7 - entry point + mode handler integration
- Tag mode routes to fetchForgejoData vs fetchGitHubData based on platform
- createInitialComment auto-detects platform for Forgejo spinner/URL format
- update-comment-link uses updateForgejoCommentBody + Forgejo PR compare URL
- update-with-branch uses platform-aware branch/job-run link formatting
- Agent mode needed NO changes (token in run.ts, rest uses Octokit REST)
- 11 new integration tests in test/m7-integration.test.ts
- 785 tests pass, typecheck clean, format clean
Progress: 78% complete (7/9 milestones) - M3, M8, M9 remaining
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
