feat(operator): command palette, impersonation, incident, tweaks (O.8)

- CommandPalette + useCommandPalette: ⌘K opens a search-and-jump panel over
  real tenants/partners + fixture flags + nav + actions. Arrow keys + Enter
  navigate, Escape/backdrop close. Recents are intentionally omitted for now;
  add when there's something to recent over.
- Impersonation stub: useImpersonation + ImpersonationModal + ImpersonationBanner.
  Modal opens from tenant detail and from the palette. Banner stays at the top
  of the shell until exited. No real OBO token is minted — wiring OAuth Token
  Exchange is tracked as a follow-up.
- IncidentModal + useIncidentModal: opened from the Overview and Infrastructure
  incident banners, renders the mock INCIDENT data with metrics, timeline and
  draft composer.
- TweaksPanel + useTweaks: floating bottom-right panel for theme (dark/light),
  density (comfy/compact), env badge (prod/staging/dev). Saved to localStorage.
- Theme/density apply via [data-theme] + [data-density] overrides in
  tokens.css. Topbar env badge now reads from useTweaks instead of a prop.
- Layout wires ⌘K + ⌘[ at the document level and mounts the palette + modals
  + banner + tweaks panel once for all pages.

apps/operator/pages/tenants/[slug].vue

@@ -10,6 +10,8 @@ const { data: tenant, refresh: refreshTenant } = await useFetch<Tenant>(() => `/
 
 const activeTab = ref<'overview' | 'users' | 'resources' | 'billing' | 'audit' | 'support' | 'danger'>('overview')
 
+const impersonate = useImpersonation()
+
 // Lazy-fetch users only when the tab is opened.
 const { data: users, refresh: refreshUsers } = useLazyFetch<TenantUser[]>(
   () => `/api/tenants/${slug.value}/users`,
@@ -97,6 +99,10 @@ async function reconcile() {
       <template #actions>
         <Badge :tone="STATUS_TONE[tenant.status]" dot>{{ tenant.status }}</Badge>
         <Badge tone="neutral">{{ tenant.plan }}</Badge>
+        <UiButton variant="secondary" @click="impersonate.open(tenant)">
+          <template #leading><UiIcon name="key" :size="13" /></template>
+          Impersonate
+        </UiButton>
         <UiButton variant="secondary">
           <template #leading><UiIcon name="external" :size="13" /></template>
           Open workspace