Story 42: Deterministic worktree management via REST/MCP API

Add REST and MCP endpoints for creating, listing, and removing worktrees.
Includes worktree lifecycle management and cleanup operations.

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

server/src/agents.rs

@@ -466,6 +466,21 @@ impl AgentPool {
         }
     }
 
+    /// Create a worktree for the given story using the server port (writes .mcp.json).
+    pub async fn create_worktree(
+        &self,
+        project_root: &Path,
+        story_id: &str,
+    ) -> Result<worktree::WorktreeInfo, String> {
+        let config = ProjectConfig::load(project_root)?;
+        worktree::create_worktree(project_root, story_id, &config, self.port).await
+    }
+
+    /// Return the port this server is running on.
+    pub fn port(&self) -> u16 {
+        self.port
+    }
+
     /// Get project root helper.
     pub fn get_project_root(
         &self,