fix(worktrees): disable selector outside git repos

Expose isGitRepo on worktree listing and show Worktree: Unavailable while disabling the dropdown when a workspace folder is not a Git repository.

packages/server/src/api-types.ts

@@ -64,6 +64,8 @@ export interface WorktreeDescriptor {
 
 export interface WorktreeListResponse {
   worktrees: WorktreeDescriptor[]
+  /** True when the workspace folder resolves to a Git repository. */
+  isGitRepo?: boolean
 }
 
 export interface WorktreeCreateRequest {

packages/server/src/server/routes/worktrees.ts

@@ -34,9 +34,9 @@ export function registerWorktreeRoutes(app: FastifyInstance, deps: RouteDeps) {
       return { error: "Workspace not found" }
     }
 
-    const { repoRoot } = await resolveRepoRoot(workspace.path, request.log)
+    const { repoRoot, isGitRepo } = await resolveRepoRoot(workspace.path, request.log)
     const worktrees = await listWorktrees({ repoRoot, workspaceFolder: workspace.path, logger: request.log })
-    const response: WorktreeListResponse = { worktrees }
+    const response: WorktreeListResponse = { worktrees, isGitRepo }
     return response
   })