feat: Redesign review tab with phase selection, commit navigation, and consolidated toolbar

- Add BranchManager.listCommits() and diffCommit() for commit-level navigation
- Add getPhaseReviewCommits and getCommitDiff tRPC procedures
- New ReviewHeader: consolidated toolbar with phase selector pills, branch info,
  stats, integrated preview controls, and approve/reject actions
- New CommitNav: horizontal commit strip with "All changes" + individual commits,
  each showing hash, message, and change stats
- Slim down ReviewSidebar: file list only with dimming for out-of-scope files
  when viewing a single commit
- ReviewTab orchestrates all pieces in a single bordered card layout

docs/server-api.md

@@ -109,6 +109,10 @@ Each procedure uses `require*Repository(ctx)` helpers that throw `TRPCError(INTE
 | listInitiativePhaseDependencies | query | All dependency edges |
 | getPhaseDependencies | query | What this phase depends on |
 | getPhaseDependents | query | What depends on this phase |
+| getPhaseReviewDiff | query | Full branch diff for pending_review phase |
+| getPhaseReviewCommits | query | List commits between initiative and phase branch |
+| getCommitDiff | query | Diff for a single commit (by hash) in a phase |
+| approvePhaseReview | mutation | Approve and merge phase branch |
 
 ### Phase Dispatch
 | Procedure | Type | Description |