chore: scaffold chatelet LNbits extension

Nostr-native room rentals (Airbnb-style) for the castle. Establishes the
extension manifest, license, README with the design overview, and static
+ template placeholders. No booking logic yet — subsequent commits build
the model, schema, arbiter, Nostr layer, API, tasks, and wiring bottom-up.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019VUQCfdqiLSsFS2jcGnaFD

static/js/index.js

@@ -0,0 +1,15 @@
+// Chatelet operator admin page — placeholder.
+// Quasar 2 + Vue 3 as UMD globals (no build step). Remember: no
+// self-closing tags in UMD templates, and use :style bindings (not <style>
+// blocks) for per-element typography overrides on LNbits pages.
+window.app = Vue.createApp({
+  el: '#vue',
+  mixins: [window.windowMixin],
+  data() {
+    return {
+      rooms: [],
+      bookings: [],
+    }
+  },
+  // TODO: wire GET /chatelet/api/v1/rooms, room CRUD, calendar, bookings.
+})