fix(tests): add missing useConnection mock to 3 test files

AudioInputNode, EaseCurveNode, and VideoStitchNode tests used manual
@xyflow/react mocks that didn't include useConnection, which is now
called by the useShowHandleLabels hook. Add the mock to fix all 40 tests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/__tests__/AudioInputNode.test.tsx

@@ -39,6 +39,7 @@ vi.mock("@xyflow/react", () => {
       setNodes: () => {},
       screenToFlowPosition: (pos: unknown) => pos,
     }),
+    useConnection: (selector: (state: { inProgress: boolean }) => boolean) => selector({ inProgress: false }),
   };
 });
 

src/components/__tests__/EaseCurveNode.test.tsx

@@ -40,6 +40,7 @@ vi.mock("@xyflow/react", () => {
       setNodes: vi.fn(),
       screenToFlowPosition: (pos: unknown) => pos,
     }),
+    useConnection: (selector: (state: { inProgress: boolean }) => boolean) => selector({ inProgress: false }),
   };
 });
 

src/components/__tests__/VideoStitchNode.test.tsx

@@ -42,6 +42,7 @@ vi.mock("@xyflow/react", () => {
       setNodes: () => {},
       screenToFlowPosition: (pos: unknown) => pos,
     }),
+    useConnection: (selector: (state: { inProgress: boolean }) => boolean) => selector({ inProgress: false }),
   };
 });