release(v1.7.36-alpha): bitcoin-core in App Store + Sovereignty Stack + dynamic catalog URL

- neode-ui/public/assets/img/app-icons/bitcoin-core.svg (NEW): 256×256
  Umbrel community Bitcoin icon sourced from getumbrel.github.io/
  umbrel-apps-gallery/bitcoin/icon.svg. Referenced by the static
  catalog, the curated fallback, and the upstream lfg2025/app-catalog
  entry so every surface shows the same image.
- app-catalog/catalog.json + neode-ui/public/catalog.json: add
  bitcoin-core (v28.4) entry pointing at bitcoin/bitcoin:28.4. Same
  entry pushed to the lfg2025/app-catalog repo on .160 and the local
  gitea mirror so nodes see it without needing a full archipelago
  update. Sovereignty Stack entry added to FEATURED_DEFINITIONS with
  a description that frames it as a Knots alternative, not a rival.
- core/archipelago/src/api/handler/mod.rs: handle_app_catalog_proxy
  is now instance-scoped (&self) and derives its upstream list from
  load_registries — each active container registry contributes one
  `<scheme>://<reg.url>/app-catalog/raw/branch/main/catalog.json` URL
  in priority order (scheme follows tls_verify). When the operator
  switches mirrors in Settings, the App Store now follows. Falls back
  to the legacy hardcoded .160/tx1138 pair only when registry config
  can't be loaded, so the App Store still renders on nodes that
  haven't persisted one yet.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app-catalog/catalog.json

@@ -1,6 +1,6 @@
 {
   "version": 2,
-  "updated": "2026-04-12T00:00:00Z",
+  "updated": "2026-04-22T00:00:00Z",
   "registry": "git.tx1138.com/lfg2025",
   "featured": {
     "id": "indeedhub",
@@ -18,6 +18,14 @@
       "dockerImage": "git.tx1138.com/lfg2025/bitcoin-knots:latest",
       "repoUrl": "https://github.com/bitcoinknots/bitcoin"
     },
+    {
+      "id": "bitcoin-core", "title": "Bitcoin Core", "version": "28.4",
+      "description": "Reference implementation of the Bitcoin protocol. Run a full node validating and relaying blocks.",
+      "icon": "/assets/img/app-icons/bitcoin-core.svg",
+      "author": "Bitcoin Core contributors", "category": "money", "tier": "optional",
+      "dockerImage": "bitcoin/bitcoin:28.4",
+      "repoUrl": "https://github.com/bitcoin/bitcoin"
+    },
     {
       "id": "lnd", "title": "LND", "version": "0.18.4",
       "description": "Lightning Network Daemon. Fast Bitcoin payments through Lightning.",