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/git-process-logging.md

@@ -43,6 +43,8 @@ Worktrees stored in `.cw-worktrees/` subdirectory of the repo. Each agent gets a
 | `deleteBranch(repoPath, branch)` | Delete local branch (no-op if missing) |
 | `branchExists(repoPath, branch)` | Check local branches |
 | `remoteBranchExists(repoPath, branch)` | Check remote tracking branches (`origin/<branch>`) |
+| `listCommits(repoPath, base, head)` | List commits head has that base doesn't (with stats) |
+| `diffCommit(repoPath, commitHash)` | Get unified diff for a single commit |
 
 `remoteBranchExists` is used by `registerProject` and `updateProject` to validate that a project's default branch actually exists in the cloned repository before saving.