test(kernel-ui): Robustify SendMessageForm tests (#924)

Use `resetMocks()` in `afterEach` instead of manual restoration at the
end of the test body, so a mid-test assertion failure cannot leave
`isKRefMock` stuck at false for subsequent tests.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk: changes are confined to a unit test file and only affect
mock reset/cleanup behavior, not production logic.
> 
> **Overview**
> Updates `SendMessageForm.test.tsx` to destructure and call
`resetMocks()` from `setupOcapKernelMock()` in `afterEach`, ensuring
mock validation flags (e.g., `isKRef`) are restored even if a test
aborts early.
> 
> Removes the in-test manual re-enabling of `isKRef` in the KRef
validation case, relying on centralized teardown for consistent test
isolation.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
3572568. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: rekmarks

packages/kernel-ui/src/components/SendMessageForm.test.tsx

@@ -17,7 +17,7 @@ import { useRegistry } from '../hooks/useRegistry.ts';
 import type { ObjectRegistry } from '../types.ts';
 import { SendMessageForm } from './SendMessageForm.tsx';
 
-const { setMockBehavior } = setupOcapKernelMock();
+const { resetMocks, setMockBehavior } = setupOcapKernelMock();
 
 vi.mock('../context/PanelContext.tsx', () => ({
   usePanelContext: vi.fn(),
@@ -109,6 +109,7 @@ describe('SendMessageForm Component', () => {
 
   afterEach(() => {
     cleanup();
+    resetMocks();
     vi.resetModules();
   });
 
@@ -203,8 +204,6 @@ describe('SendMessageForm Component', () => {
     // Target should remain unset, button stays disabled
     expect(targetSelect).toHaveValue('');
     expect(getByTestId('message-send-button')).toBeDisabled();
-
-    setMockBehavior({ isKRef: true });
   });
 
   it('calls callKernelMethod with correct parameters when Send button is clicked', async () => {