fix(canvas): Save button no-op due to leaked click event

The Toolbar and Sidebar Save buttons wired onClick={onSave} directly, so
React passed the MouseEvent as the first argument. handleSave treats its
first arg as a designIdOverride, corrupting design_id and making the save
fail silently. Ctrl+S worked because it calls handleSave() with no args.

Wrap both handlers as onClick={() => onSave()} so no event leaks through.

Add regression tests asserting onSave is called with zero arguments.

Fixes #186

ha-relevant: no

frontend/src/components/panels/__tests__/Toolbar.test.tsx

@@ -0,0 +1,59 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest'
+import { render, screen, fireEvent } from '@testing-library/react'
+import { Toolbar } from '../Toolbar'
+import { useCanvasStore } from '@/stores/canvasStore'
+
+// ── Mocks ────────────────────────────────────────────────────────────────────
+
+vi.mock('@/stores/canvasStore')
+
+vi.mock('@/components/ui/Logo', () => ({
+  Logo: () => <div data-testid="logo" />,
+}))
+
+function mockStore(overrides: Partial<ReturnType<typeof useCanvasStore>> = {}) {
+  vi.mocked(useCanvasStore).mockReturnValue({
+    hasUnsavedChanges: false,
+    past: [],
+    future: [],
+    ...overrides,
+  } as ReturnType<typeof useCanvasStore>)
+}
+
+const defaultProps = {
+  onSave: vi.fn(),
+  onAutoLayout: vi.fn(),
+  onExport: vi.fn(),
+  onChangeStyle: vi.fn(),
+  onUndo: vi.fn(),
+  onRedo: vi.fn(),
+  onShortcuts: vi.fn(),
+  onExportMd: vi.fn(),
+  onExportYaml: vi.fn(),
+  onImportYaml: vi.fn(),
+  onViewOnly: vi.fn(),
+}
+
+// ── Tests ─────────────────────────────────────────────────────────────────────
+
+describe('Toolbar', () => {
+  beforeEach(() => {
+    mockStore()
+    vi.clearAllMocks()
+  })
+
+  it('calls onSave when Save is clicked', () => {
+    render(<Toolbar {...defaultProps} />)
+    fireEvent.click(screen.getByText('Save'))
+    expect(defaultProps.onSave).toHaveBeenCalledOnce()
+  })
+
+  // Regression (#186): the click handler must not forward the MouseEvent as an
+  // argument — handleSave treats its first arg as a designIdOverride, so leaking
+  // the event corrupts design_id and the save silently fails.
+  it('calls onSave with no arguments (does not leak the click event)', () => {
+    render(<Toolbar {...defaultProps} />)
+    fireEvent.click(screen.getByText('Save'))
+    expect(defaultProps.onSave).toHaveBeenCalledWith()
+  })
+})