fix: resolve JS-005, JS-006, SVC-006 architecture violations

- JS-005: Add initialization guards to email-templates.js (admin/vendor)
- JS-006: Add try/catch error handling to content-pages.js init
- SVC-006: Move db.commit() from services to endpoints for proper
  transaction control in email_template_service and vendor_team_service

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

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

static/vendor/js/email-templates.js

@@ -54,6 +54,9 @@ function vendorEmailTemplates() {
 
         // Lifecycle
         async init() {
+            if (window._vendorEmailTemplatesInitialized) return;
+            window._vendorEmailTemplatesInitialized = true;
+
             vendorEmailTemplatesLog.info('Email templates init() called');
 
             // Call parent init to set vendorCode and other base state