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

apps/server/git/branch-manager.ts

@@ -6,7 +6,7 @@
  * a worktree to be checked out.
  */
 
-import type { MergeResult } from './types.js';
+import type { MergeResult, BranchCommit } from './types.js';
 
 export interface BranchManager {
   /**
@@ -45,4 +45,15 @@ export interface BranchManager {
    * since local branches may not include all remote branches.
    */
   remoteBranchExists(repoPath: string, branch: string): Promise<boolean>;
+
+  /**
+   * List commits that headBranch has but baseBranch doesn't.
+   * Used for commit-level navigation in code review.
+   */
+  listCommits(repoPath: string, baseBranch: string, headBranch: string): Promise<BranchCommit[]>;
+
+  /**
+   * Get the raw unified diff for a single commit.
+   */
+  diffCommit(repoPath: string, commitHash: string): Promise<string>;
 }

apps/server/git/simple-git-branch-manager.ts

@@ -11,7 +11,7 @@ import { mkdtempSync, rmSync } from 'node:fs';
 import { tmpdir } from 'node:os';
 import { simpleGit } from 'simple-git';
 import type { BranchManager } from './branch-manager.js';
-import type { MergeResult } from './types.js';
+import type { MergeResult, BranchCommit } from './types.js';
 import { createModuleLogger } from '../logger/index.js';
 
 const log = createModuleLogger('branch-manager');
@@ -116,4 +116,28 @@ export class SimpleGitBranchManager implements BranchManager {
       return false;
     }
   }
+
+  async listCommits(repoPath: string, baseBranch: string, headBranch: string): Promise<BranchCommit[]> {
+    const git = simpleGit(repoPath);
+    const logResult = await git.log({ from: baseBranch, to: headBranch, '--stat': null });
+
+    return logResult.all.map((entry) => {
+      const diffStat = entry.diff;
+      return {
+        hash: entry.hash,
+        shortHash: entry.hash.slice(0, 7),
+        message: entry.message,
+        author: entry.author_name,
+        date: entry.date,
+        filesChanged: diffStat?.files?.length ?? 0,
+        insertions: diffStat?.insertions ?? 0,
+        deletions: diffStat?.deletions ?? 0,
+      };
+    });
+  }
+
+  async diffCommit(repoPath: string, commitHash: string): Promise<string> {
+    const git = simpleGit(repoPath);
+    return git.diff([`${commitHash}~1`, commitHash]);
+  }
 }

apps/server/git/types.ts

@@ -58,6 +58,33 @@ export interface MergeResult {
   message: string;
 }
 
+// =============================================================================
+// Branch Commit Info
+// =============================================================================
+
+/**
+ * Represents a single commit in a branch's history.
+ * Used for commit-level navigation in code review.
+ */
+export interface BranchCommit {
+  /** Full commit hash */
+  hash: string;
+  /** Short commit hash (7 chars) */
+  shortHash: string;
+  /** First line of commit message */
+  message: string;
+  /** Author name */
+  author: string;
+  /** ISO date string */
+  date: string;
+  /** Number of files changed */
+  filesChanged: number;
+  /** Number of insertions */
+  insertions: number;
+  /** Number of deletions */
+  deletions: number;
+}
+
 // =============================================================================
 // WorktreeManager Port Interface
 // =============================================================================