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/http/mcp.rs

@@ -1,4 +1,4 @@
-use crate::agents::{close_bug_to_archive, move_story_to_archived, move_story_to_merge};
+use crate::agents::{close_bug_to_archive, move_story_to_archived, move_story_to_merge, move_story_to_qa};
 use crate::config::ProjectConfig;
 use crate::http::context::AppContext;
 use crate::http::settings::get_editor_command_from_store;
@@ -742,6 +742,24 @@ fn handle_tools_list(id: Option<Value>) -> JsonRpcResponse {
                         },
                         "required": ["story_id"]
                     }
+                },
+                {
+                    "name": "request_qa",
+                    "description": "Trigger QA review of a completed story worktree: moves the item from work/2_current/ to work/3_qa/ and starts the qa agent to run quality gates, tests, and generate a manual testing plan.",
+                    "inputSchema": {
+                        "type": "object",
+                        "properties": {
+                            "story_id": {
+                                "type": "string",
+                                "description": "Story identifier (e.g. '53_story_qa_agent_role')"
+                            },
+                            "agent_name": {
+                                "type": "string",
+                                "description": "Agent name to use for QA (defaults to 'qa')"
+                            }
+                        },
+                        "required": ["story_id"]
+                    }
                 }
             ]
         }),
@@ -797,6 +815,8 @@ async fn handle_tools_call(
         // Mergemaster tools
         "merge_agent_work" => tool_merge_agent_work(&args, ctx).await,
         "move_story_to_merge" => tool_move_story_to_merge(&args, ctx),
+        // QA tools
+        "request_qa" => tool_request_qa(&args, ctx).await,
         _ => Err(format!("Unknown tool: {tool_name}")),
     };
 
@@ -1360,6 +1380,42 @@ fn tool_move_story_to_merge(args: &Value, ctx: &AppContext) -> Result<String, St
     ))
 }
 
+// ── QA tool implementations ───────────────────────────────────────
+
+async fn tool_request_qa(args: &Value, ctx: &AppContext) -> Result<String, String> {
+    let story_id = args
+        .get("story_id")
+        .and_then(|v| v.as_str())
+        .ok_or("Missing required argument: story_id")?;
+    let agent_name = args
+        .get("agent_name")
+        .and_then(|v| v.as_str())
+        .unwrap_or("qa");
+
+    let project_root = ctx.agents.get_project_root(&ctx.state)?;
+
+    // Move story from work/2_current/ to work/3_qa/
+    move_story_to_qa(&project_root, story_id)?;
+
+    // Start the QA agent on the story worktree
+    let info = ctx
+        .agents
+        .start_agent(&project_root, story_id, Some(agent_name))
+        .await?;
+
+    serde_json::to_string_pretty(&json!({
+        "story_id": info.story_id,
+        "agent_name": info.agent_name,
+        "status": info.status.to_string(),
+        "worktree_path": info.worktree_path,
+        "message": format!(
+            "Story '{story_id}' moved to work/3_qa/ and QA agent '{}' started.",
+            info.agent_name
+        ),
+    }))
+    .map_err(|e| format!("Serialization error: {e}"))
+}
+
 /// Run `git log <base>..HEAD --oneline` in the worktree and return the commit
 /// summaries, or `None` if git is unavailable or there are no new commits.
 async fn get_worktree_commits(worktree_path: &str, base_branch: &str) -> Option<Vec<String>> {
@@ -1519,7 +1575,8 @@ mod tests {
         assert!(names.contains(&"close_bug"));
         assert!(names.contains(&"merge_agent_work"));
         assert!(names.contains(&"move_story_to_merge"));
-        assert_eq!(tools.len(), 26);
+        assert!(names.contains(&"request_qa"));
+        assert_eq!(tools.len(), 27);
     }
 
     #[test]