Add breathing room when focusing comment composer

Co-Authored-By: Paperclip <noreply@paperclip.ing>

ui/src/components/IssueChatThread.test.tsx

@@ -293,6 +293,7 @@ describe("IssueChatThread", () => {
   it("exposes a composer focus handle that forwards to the editor", () => {
     const root = createRoot(container);
     const composerRef = createRef<{ focus: () => void }>();
+    const scrollByMock = vi.spyOn(window, "scrollBy").mockImplementation(() => {});
     const requestAnimationFrameMock = vi
       .spyOn(window, "requestAnimationFrame")
       .mockImplementation((callback: FrameRequestCallback) => {
@@ -328,7 +329,9 @@ describe("IssueChatThread", () => {
     });
 
     expect(scrollIntoViewMock).toHaveBeenCalledWith({ behavior: "smooth", block: "end" });
+    expect(scrollByMock).toHaveBeenCalledWith({ top: 96, behavior: "smooth" });
     expect(markdownEditorFocusMock).toHaveBeenCalledTimes(1);
+    scrollByMock.mockRestore();
     requestAnimationFrameMock.mockRestore();
 
     act(() => {

ui/src/components/IssueChatThread.tsx

@@ -219,6 +219,7 @@ interface IssueChatThreadProps {
 }
 
 const DRAFT_DEBOUNCE_MS = 800;
+const COMPOSER_FOCUS_SCROLL_PADDING_PX = 96;
 
 function toIsoString(value: string | Date | null | undefined): string | null {
   if (!value) return null;
@@ -1443,6 +1444,7 @@ const IssueChatComposer = forwardRef<IssueChatComposerHandle, IssueChatComposerP
     focus: () => {
       composerContainerRef.current?.scrollIntoView({ behavior: "smooth", block: "end" });
       requestAnimationFrame(() => {
+        window.scrollBy({ top: COMPOSER_FOCUS_SCROLL_PADDING_PX, behavior: "smooth" });
         editorRef.current?.focus();
       });
     },