fix: extend TPL-009 to vendor templates and fix billing data inheritance

- Extended TPL-009 architecture rule to check vendor templates for invalid
  block names (was only checking admin templates)
- Fixed billing.js to inherit base Alpine data via ...data() spread,
  resolving undefined errors for dark, isSideMenuOpen, vendorCode

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

static/vendor/js/billing.js

@@ -5,6 +5,9 @@ const billingLog = window.LogConfig?.createLogger('BILLING') || console;
 
 function billingData() {
     return {
+        // Inherit base data (dark mode, sidebar, vendor info, etc.)
+        ...data(),
+
         // State
         loading: true,
         subscription: null,