v5.3.7: Fix sync stall, transaction display, balance updates, and bootstrap snapshots

Sync fixes:
- Extend stall detection beyond IBD to catch post-IBD sync gaps
- Walk-forward inv continuation to avoid CBlockLocator exponential gap loop
- Track walk-forward progress for stall recovery without restarting from scratch

GUI fixes:
- Load transactions synchronously in constructor (deferred QTimer never fired)
- Use beginResetModel/endResetModel instead of deprecated reset()
- Schedule full refresh on TRY_LOCK failure to avoid dropped CT_NEW notifications
- Only update cachedNumBlocks after successful balance check (prevents permanent loss)
- Add GetAllBalances() single-pass balance retrieval with TRY_LOCK

Bootstrap:
- Add trusted snapshot manifest verification for bootstrap archives
- Add IsKnownCheckpoint() to validate manifest against compiled-in checkpoints
- Skip txleveldb rebuild when verified manifest is present

Bump version to 5.3.7 across all packaging manifests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packaging/appstream/org.cryptographic_triangles.TrianglesQt.metainfo.xml

@@ -41,6 +41,11 @@
   </provides>
 
   <releases>
+    <release version="5.3.7" date="2026-03-24">
+      <description>
+        <p>Version 5.3.7 release.</p>
+      </description>
+    </release>
     <release version="5.3.6" date="2026-03-23">
       <description>
         <p>IBD sync optimizations, Linux build fixes, and modern compiler support.</p>