feat(FN-947): show files-changed on done column task cards

- Extend useSessionFiles hook to fetch files for done column tasks
- Update TaskCard to display files-changed indicator on done column cards
- Add tests for useSessionFiles done column support
- Add tests for TaskCard files-changed display in done column

packages/dashboard/app/hooks/__tests__/useSessionFiles.test.ts

@@ -50,4 +50,24 @@ describe("useSessionFiles", () => {
 
     expect(result.current.files).toEqual([]);
   });
+
+  it("fetches session files for done column tasks with a worktree", async () => {
+    mockFetchSessionFiles.mockResolvedValueOnce(["src/x.ts", "src/y.ts", "src/z.ts"]);
+
+    const { result } = renderHook(() => useSessionFiles("FN-456", "/repo/.worktrees/kb-456", "done"));
+
+    await waitFor(() => expect(result.current.loading).toBe(false));
+
+    expect(result.current.files).toEqual(["src/x.ts", "src/y.ts", "src/z.ts"]);
+    expect(mockFetchSessionFiles).toHaveBeenCalledWith("FN-456", undefined);
+  });
+
+  it("does not fetch for done column tasks without a worktree", async () => {
+    const { result } = renderHook(() => useSessionFiles("FN-456", undefined, "done"));
+
+    await waitFor(() => expect(result.current.loading).toBe(false));
+
+    expect(result.current.files).toEqual([]);
+    expect(mockFetchSessionFiles).not.toHaveBeenCalled();
+  });
 });

packages/dashboard/app/hooks/useSessionFiles.ts

@@ -1,7 +1,7 @@
 import { useEffect, useState } from "react";
 import { fetchSessionFiles } from "../api";
 
-const ACTIVE_COLUMNS = new Set(["in-progress", "in-review"]);
+const ACTIVE_COLUMNS = new Set(["in-progress", "in-review", "done"]);
 
 interface UseSessionFilesResult {
   files: string[];