fix(dashboard): translate chat thread to follow iOS visual viewport offset

After sending on mobile the iOS Safari focus retention shifts
visualViewport.offsetTop, leaving the composer near the top of the
screen. Translate the chat thread by that offset so it stays pinned
above the keyboard.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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

@@ -2537,6 +2537,47 @@ describe("ChatView mobile behavior", () => {
     }
   });
 
+  it("mobile mode: does not force window scroll when keyboard opens", async () => {
+    const restoreMatchMedia = mockMobileViewport();
+    const { listeners, mockVV } = mockMobileVisualViewport({
+      innerHeight: 800,
+      vvHeight: 800,
+    });
+
+    const scrollToSpy = vi.spyOn(window, "scrollTo").mockImplementation(() => {});
+
+    try {
+      setupMockChat({
+        activeSession: activeSessionFixture,
+        messages: [{ id: "msg-001", sessionId: "session-001", role: "assistant", content: "Hello", createdAt: "2026-04-08T00:00:00.000Z" }],
+      });
+
+      render(<ChatView projectId="proj-123" addToast={vi.fn()} />);
+
+      Object.defineProperty(window, "innerHeight", {
+        value: 560,
+        writable: true,
+        configurable: true,
+      });
+      Object.defineProperty(mockVV, "height", {
+        value: 560,
+        writable: true,
+        configurable: true,
+      });
+
+      act(() => {
+        for (const cb of listeners.resize) cb();
+      });
+
+      await waitFor(() => {
+        expect(scrollToSpy).not.toHaveBeenCalled();
+      });
+    } finally {
+      scrollToSpy.mockRestore();
+      restoreMatchMedia.mockRestore();
+    }
+  });
+
   it("mobile mode: does not subscribe to keyboard tracking without active session", async () => {
     const restoreMatchMedia = mockMobileViewport();
     const { mockVV } = mockMobileVisualViewport({