Story 53: Add QA agent role with request_qa MCP tool

- Add `qa` agent entry to `.story_kit/project.toml` with a detailed
  prompt covering code quality scan, test verification, manual testing
  support, and structured report generation
- Add `move_story_to_qa` function in `agents.rs` that moves a work item
  from `work/2_current/` to `work/3_qa/` and auto-commits (idempotent)
- Add `request_qa` MCP tool in `mcp.rs` that moves the story to
  `work/3_qa/` and starts the QA agent on the existing worktree
- Add unit tests for `move_story_to_qa` (moves, idempotent, error cases)
- Update `tools_list_returns_all_tools` test to expect 27 tools

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/src/agents.rs

@@ -943,6 +943,42 @@ pub fn move_story_to_merge(project_root: &Path, story_id: &str) -> Result<(), St
     )
 }
 
+/// Move a story/bug from `work/2_current/` to `work/3_qa/` and auto-commit.
+///
+/// This stages a work item for QA review before merging to master.
+/// Idempotent: if already in `3_qa/`, returns Ok without committing.
+pub fn move_story_to_qa(project_root: &Path, story_id: &str) -> Result<(), String> {
+    let sk = project_root.join(".story_kit").join("work");
+    let current_path = sk.join("2_current").join(format!("{story_id}.md"));
+    let qa_dir = sk.join("3_qa");
+    let qa_path = qa_dir.join(format!("{story_id}.md"));
+
+    if qa_path.exists() {
+        // Already in 3_qa/ — idempotent, nothing to do.
+        return Ok(());
+    }
+
+    if !current_path.exists() {
+        return Err(format!(
+            "Work item '{story_id}' not found in work/2_current/. Cannot move to 3_qa/."
+        ));
+    }
+
+    std::fs::create_dir_all(&qa_dir)
+        .map_err(|e| format!("Failed to create work/3_qa/ directory: {e}"))?;
+    std::fs::rename(&current_path, &qa_path)
+        .map_err(|e| format!("Failed to move '{story_id}' to 3_qa/: {e}"))?;
+
+    eprintln!("[lifecycle] Moved '{story_id}' from work/2_current/ to work/3_qa/");
+
+    let msg = format!("story-kit: queue {story_id} for QA");
+    git_stage_and_commit(
+        project_root,
+        &[qa_path.as_path(), current_path.as_path()],
+        &msg,
+    )
+}
+
 /// Move a bug from `work/2_current/` or `work/1_upcoming/` to `work/5_archived/` and auto-commit.
 ///
 /// * If the bug is in `2_current/`, it is moved to `5_archived/` and committed.
@@ -1901,6 +1937,75 @@ mod tests {
         assert!(result.unwrap_err().contains("not found in work/2_current/"));
     }
 
+    // ── move_story_to_qa tests ────────────────────────────────────────────────
+
+    #[test]
+    fn move_story_to_qa_moves_file_and_commits() {
+        use std::fs;
+        use tempfile::tempdir;
+
+        let tmp = tempdir().unwrap();
+        let repo = tmp.path();
+        init_git_repo(repo);
+
+        let current_dir = repo.join(".story_kit/work/2_current");
+        fs::create_dir_all(&current_dir).unwrap();
+        let story_file = current_dir.join("30_story_qa_test.md");
+        fs::write(&story_file, "---\nname: QA Test\ntest_plan: approved\n---\n").unwrap();
+
+        Command::new("git")
+            .args(["add", "."])
+            .current_dir(repo)
+            .output()
+            .unwrap();
+        Command::new("git")
+            .args(["commit", "-m", "add story"])
+            .current_dir(repo)
+            .output()
+            .unwrap();
+
+        move_story_to_qa(repo, "30_story_qa_test").unwrap();
+
+        let qa_path = repo.join(".story_kit/work/3_qa/30_story_qa_test.md");
+        assert!(!story_file.exists(), "2_current file should be gone");
+        assert!(qa_path.exists(), "3_qa file should exist");
+    }
+
+    #[test]
+    fn move_story_to_qa_idempotent_when_already_in_qa() {
+        use std::fs;
+        use tempfile::tempdir;
+
+        let tmp = tempdir().unwrap();
+        let repo = tmp.path();
+        init_git_repo(repo);
+
+        let qa_dir = repo.join(".story_kit/work/3_qa");
+        fs::create_dir_all(&qa_dir).unwrap();
+        fs::write(
+            qa_dir.join("31_story_test.md"),
+            "---\nname: Test\ntest_plan: approved\n---\n",
+        )
+        .unwrap();
+
+        // Should succeed without error even though there's nothing to move
+        move_story_to_qa(repo, "31_story_test").unwrap();
+        assert!(qa_dir.join("31_story_test.md").exists());
+    }
+
+    #[test]
+    fn move_story_to_qa_errors_when_not_in_current() {
+        use tempfile::tempdir;
+
+        let tmp = tempdir().unwrap();
+        let repo = tmp.path();
+        init_git_repo(repo);
+
+        let result = move_story_to_qa(repo, "99_nonexistent");
+        assert!(result.is_err());
+        assert!(result.unwrap_err().contains("not found in work/2_current/"));
+    }
+
     // ── move_story_to_archived with 4_merge source ────────────────────────────
 
     #[test]