fix(bitcoin): knots catalog default must equal top-level version

The knots versions[] marked 29.3.knots20260508 as default while the
top-level catalog version is the floating 'latest' tag — violating the
generator's own invariant (default:true MUST equal the top-level version
so selecting it un-pins / tracks latest). Live effect via package.versions:
catalog_default_version='latest' so the UI-highlighted default actually
PINS+recreates (opposite of un-pin) and 'latest' was unreachable from the
Version & Updates card.

Add a 'latest' default entry (== the manifest's floating tag) and keep
29.3.knots20260508 as a pinnable option. Verified on .228: package.versions
now returns default=latest with 2 selectable versions.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

releases/app-catalog.json

@@ -568,9 +568,13 @@
       },
       "versions": [
         {
-          "version": "29.3.knots20260508",
-          "image": "146.59.87.168:3000/lfg2025/bitcoin-knots:29.3.knots20260508",
+          "version": "latest",
+          "image": "146.59.87.168:3000/lfg2025/bitcoin-knots:latest",
           "default": true
+        },
+        {
+          "version": "29.3.knots20260508",
+          "image": "146.59.87.168:3000/lfg2025/bitcoin-knots:29.3.knots20260508"
         }
       ]
     },