feat(FN-1019): reflow Changes-tab header stats and fix terminal scrollback

- Reflow Changes-tab header stats to a second line for better layout
- Add CSS styles for two-line header stats display
- Fix useTerminal hook to clear buffered scrollback after first subscriber replay
- Add tests for TaskChangesTab header stats rendering
- Update README description for Changes tab header

packages/dashboard/app/components/TaskChangesTab.tsx

@@ -196,14 +196,16 @@ export function TaskChangesTab({ taskId, worktree, projectId, column, mergeDetai
       )}
 
       <div className="changes-header">
-        <h4>
-          <FileCode size={16} />
-          Files Changed ({stats.filesChanged})
-          <span className="changes-stat-summary">
+        <div className="task-changes-header-title">
+          <h4>
+            <FileCode size={16} />
+            Files Changed ({stats.filesChanged})
+          </h4>
+          <span className="task-changes-stats changes-stat-summary">
             <span className="diff-add">+{stats.additions}</span>{" "}
             <span className="diff-del">-{stats.deletions}</span>
           </span>
-        </h4>
+        </div>
         <div className="changes-header-actions-wrapper">
           <div className="changes-header-actions">
             {files.length > 0 && (

packages/dashboard/app/components/__tests__/TaskChangesTab.test.tsx

@@ -216,6 +216,39 @@ describe("TaskChangesTab — commit-backed (done tasks)", () => {
     expect(screen.getByText("-0")).toBeTruthy();
   });
 
+  it("renders stat summary on a separate line from Files Changed title", async () => {
+    mockFetchTaskDiff.mockResolvedValue(DONE_TASK_DIFF);
+
+    const { container } = render(
+      <TaskChangesTab
+        taskId="FN-001"
+        worktree={undefined}
+        column="done"
+        mergeDetails={MERGE_DETAILS}
+      />,
+    );
+
+    await waitFor(() => {
+      expect(screen.getByText("Files Changed (2)")).toBeTruthy();
+    });
+
+    // The title and stats should be in a dedicated wrapper
+    const titleWrapper = container.querySelector(".task-changes-header-title");
+    expect(titleWrapper).toBeTruthy();
+
+    // The h4 should contain "Files Changed (N)" but NOT the stat summary
+    const h4 = titleWrapper?.querySelector("h4");
+    expect(h4).toBeTruthy();
+    expect(h4?.textContent).toContain("Files Changed (2)");
+    expect(h4?.querySelector(".changes-stat-summary")).toBeNull();
+
+    // The stat summary should be a sibling of h4, not a child
+    const statSummary = titleWrapper?.querySelector(".task-changes-stats");
+    expect(statSummary).toBeTruthy();
+    expect(statSummary?.querySelector(".diff-add")?.textContent).toBe("+3");
+    expect(statSummary?.querySelector(".diff-del")?.textContent).toBe("-0");
+  });
+
   it("toggling file expansion shows/hides diff content", async () => {
     mockFetchTaskDiff.mockResolvedValue(DONE_TASK_DIFF);
     const { container } = render(