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/composables/useCommandPalette.ts

@@ -0,0 +1,19 @@
+// Shared open/close state for the ⌘K command palette. The trigger lives on
+// the topbar and on the global keyboard shortcut handler, while the rendered
+// panel lives in the default layout — they all read/write the same ref via
+// this composable.
+
+const isOpen = ref(false)
+
+export const useCommandPalette = () => ({
+  isOpen,
+  open: () => {
+    isOpen.value = true
+  },
+  close: () => {
+    isOpen.value = false
+  },
+  toggle: () => {
+    isOpen.value = !isOpen.value
+  },
+})