fix(catalog): prefix bitcoin-core image with docker.io/ so the install validator accepts it

The trusted-registry allowlist in api/rpc/package/config.rs splits the
image on '/' and matches the first segment against a fixed set (docker.io,
ghcr.io, git.tx1138.com, 23.182.128.160:3000, ghcr.io, localhost). A bare
'bitcoin/bitcoin:28.4' splits to registry="bitcoin" which isn't on the
list, so the install RPC was returning 'Invalid Docker image format'.

Live catalogs on .160 and gitea-local already hotfixed directly; these
static copies keep ISO builds and the final hardcoded fallback in sync.

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

app-catalog/catalog.json

@@ -23,7 +23,7 @@
       "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",
+      "dockerImage": "docker.io/bitcoin/bitcoin:28.4",
       "repoUrl": "https://github.com/bitcoin/bitcoin"
     },
     {