MAESTRO: Implement Phase 7.8 - Add component tests for capability gating

Added comprehensive tests verifying that UI features are correctly hidden
when agent capabilities are false. New test covers supportsReadOnlyMode
capability which was the only gap in coverage.

Coverage summary:
- InputArea: supportsImageInput, supportsSlashCommands, supportsReadOnlyMode
- MainPanel: supportsSessionStorage, supportsSessionId, supportsCostTracking, supportsUsageStats

All 10,890 tests pass.

src/__tests__/renderer/components/InputArea.test.tsx

@@ -292,6 +292,41 @@ describe('InputArea', () => {
       expect(toggle).toHaveTextContent('Read-only');
     });
 
+    it('hides read-only toggle when agent does not support read-only mode', async () => {
+      // Mock capabilities to return false for supportsReadOnlyMode
+      const useAgentCapabilitiesMock = await import('../../../renderer/hooks/useAgentCapabilities');
+      vi.mocked(useAgentCapabilitiesMock.useAgentCapabilities).mockReturnValueOnce({
+        capabilities: {
+          supportsResume: true,
+          supportsReadOnlyMode: false, // Not supported
+          supportsJsonOutput: true,
+          supportsSessionId: true,
+          supportsImageInput: true,
+          supportsSlashCommands: true,
+          supportsSessionStorage: false,
+          supportsCostTracking: false,
+          supportsUsageStats: false,
+          supportsBatchMode: false,
+          supportsStreaming: true,
+          supportsResultMessages: true,
+        },
+        loading: false,
+        error: null,
+        refresh: vi.fn(),
+        hasCapability: vi.fn((cap: string) => cap !== 'supportsReadOnlyMode'),
+      });
+
+      const onToggleTabReadOnlyMode = vi.fn();
+      const props = createDefaultProps({
+        session: createMockSession({ inputMode: 'ai', toolType: 'opencode' }),
+        onToggleTabReadOnlyMode,
+      });
+      render(<InputArea {...props} />);
+
+      // Read-only toggle should not be present
+      expect(screen.queryByTitle(/Toggle read-only mode/)).not.toBeInTheDocument();
+    });
+
     it('shows save to history toggle when onToggleTabSaveToHistory is provided', () => {
       const onToggleTabSaveToHistory = vi.fn();
       const props = createDefaultProps({