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/index.vue

@@ -8,6 +8,8 @@ const { data: tenants, pending: tp, refresh: rT } = await useFetch<Tenant[]>('/a
 const { data: partners, pending: pp, refresh: rP } = await useFetch<Partner[]>('/api/partners', { default: () => [] })
 const { data: users, pending: up, refresh: rU } = await useFetch<PlatformUser[]>('/api/users', { default: () => [] })
 
+const { open: openIncident } = useIncidentModal()
+
 const pending = computed(() => tp.value || pp.value || up.value)
 
 async function refresh() {
@@ -63,7 +65,7 @@ function fmtDate(d: string) {
     </PageHeader>
 
     <div class="stage">
-      <button v-if="incidentActive" class="incident" type="button">
+      <button v-if="incidentActive" class="incident" type="button" @click="openIncident">
         <span class="pill">
           <span class="dot" />
           {{ INCIDENT.severity }} · ACTIVE