feat(layout): context-switcher for multi-role users

Adds components/shared/ContextSwitcher.vue — a Vuetify menu-button
that renders only when useAuthStore.showContextSwitcher is true (i.e.
the user has both portal and organizer contexts available). Click
calls useAuthStore.setLastContext + resolveLandingRoute and pushes
the new route.

Wired into both layouts:
- PortalLayout.vue: navbar right section, before UserAvatarMenu
- DefaultLayoutWithVerticalNav.vue (organizer navbar host): before
  NavbarThemeSwitcher (OrganizerLayout.vue itself is a 10-line
  wrapper around DefaultLayoutWithVerticalNav, so the component
  wires into the actual navbar host).

Boundaries matrix update: components-shared now allows `stores` so
canonical shared chrome (ContextSwitcher, future global indicators)
can read useAuthStore directly without re-homing to
components/layout/. stores-portal stays disallowed for components-
shared by design — portal-specific state has no place in shared
chrome.

Adds 3 vitest specs covering: visibility gated by
showContextSwitcher, click invokes setLastContext + router.push.

Test count 189 → 192. Frontend lint + typecheck clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/app/src/components/shared/__tests__/ContextSwitcher.spec.ts

@@ -0,0 +1,72 @@
+import { describe, expect, it, vi } from 'vitest'
+import { mount } from '@vue/test-utils'
+
+const mockSetLastContext = vi.fn()
+const mockResolveLandingRoute = vi.fn(() => ({ path: '/portal/evenementen' }))
+const mockPush = vi.fn()
+
+const authStoreState: Record<string, unknown> = {
+  showContextSwitcher: true,
+  setLastContext: mockSetLastContext,
+  resolveLandingRoute: mockResolveLandingRoute,
+}
+
+vi.mock('@/stores/useAuthStore', () => ({
+  useAuthStore: () => authStoreState,
+}))
+
+vi.mock('vue-router', async importOriginal => ({
+  ...(await importOriginal<typeof import('vue-router')>()),
+  useRoute: () => ({ meta: { context: 'organizer' } }),
+  useRouter: () => ({ push: mockPush }),
+}))
+
+const ContextSwitcher = (await import('../ContextSwitcher.vue')).default
+
+const stubs = {
+  VMenu: { template: '<div data-test="menu"><slot name="activator" :props="{}" /><slot /></div>' },
+  VBtn: { template: '<button><slot /></button>' },
+  VList: { template: '<div><slot /></div>' },
+  VListItem: {
+    props: ['dataTest'],
+    template: '<div :data-test="dataTest" @click="$emit(\'click\')"><slot /></div>',
+    emits: ['click'],
+  },
+  VListItemTitle: { template: '<span><slot /></span>' },
+  VIcon: true,
+}
+
+describe('ContextSwitcher', () => {
+  it('renders when showContextSwitcher is true', () => {
+    authStoreState.showContextSwitcher = true
+
+    const wrapper = mount(ContextSwitcher, { global: { stubs } })
+
+    expect(wrapper.find('[data-test="menu"]').exists()).toBe(true)
+  })
+
+  it('does not render when showContextSwitcher is false (single-context user)', () => {
+    authStoreState.showContextSwitcher = false
+
+    const wrapper = mount(ContextSwitcher, { global: { stubs } })
+
+    expect(wrapper.find('[data-test="menu"]').exists()).toBe(false)
+  })
+
+  it('clicking the alternative context calls setLastContext and router.push', async () => {
+    authStoreState.showContextSwitcher = true
+    mockSetLastContext.mockClear()
+    mockResolveLandingRoute.mockClear()
+    mockPush.mockClear()
+
+    const wrapper = mount(ContextSwitcher, { global: { stubs } })
+
+    // current context is 'organizer' (from mocked route.meta.context),
+    // so the dropdown shows 'switch-to-portal'.
+    await wrapper.find('[data-test="switch-to-portal"]').trigger('click')
+
+    expect(mockSetLastContext).toHaveBeenCalledWith('portal')
+    expect(mockResolveLandingRoute).toHaveBeenCalledWith('portal')
+    expect(mockPush).toHaveBeenCalledWith({ path: '/portal/evenementen' })
+  })
+})