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

config.json

@@ -0,0 +1,23 @@
+{
+  "id": "chatelet",
+  "version": "0.1.0",
+  "name": "Chatelet",
+  "repo": "https://git.atitlan.io/aiolabs/chatelet",
+  "short_description": "Nostr-native room rentals (Airbnb-style) for LNbits",
+  "description": "",
+  "tile": "/chatelet/static/image/chatelet.png",
+  "min_lnbits_version": "1.4.0",
+  "contributors": [
+    {
+      "name": "padreug",
+      "uri": "https://git.atitlan.io/padreug",
+      "role": "Author"
+    }
+  ],
+  "images": [],
+  "license": "MIT",
+  "paid_features": "",
+  "tags": ["Merchant", "Nostr"],
+  "donate": "",
+  "hidden": false
+}