perf: add defer to scripts and lazy loading to images

Add defer attribute to 145 <script> tags across 103 template files
(PERF-067) and loading="lazy" to 22 <img> tags across 13 template
files (PERF-058). Both improve page load performance.

Validator totals: 0 errors, 2 warnings, 1360 info (down from 1527).

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

app/templates/merchant/base.html

@@ -41,19 +41,19 @@
     <!-- Core Scripts - ORDER MATTERS! -->
 
     <!-- 1. FIRST: Log Configuration -->
-    <script src="{{ url_for('static', path='shared/js/log-config.js') }}"></script>
+    <script defer src="{{ url_for('static', path='shared/js/log-config.js') }}"></script>
 
     <!-- 2. SECOND: Icons (before Alpine.js) -->
-    <script src="{{ url_for('static', path='shared/js/icons.js') }}"></script>
+    <script defer src="{{ url_for('static', path='shared/js/icons.js') }}"></script>
 
     <!-- 3. THIRD: Alpine.js Base Data -->
     <script src="{{ url_for('core_static', path='merchant/js/init-alpine.js') }}"></script>
 
     <!-- 4. FOURTH: Utils (standalone utilities) -->
-    <script src="{{ url_for('static', path='shared/js/utils.js') }}"></script>
+    <script defer src="{{ url_for('static', path='shared/js/utils.js') }}"></script>
 
     <!-- 5. FIFTH: API Client (depends on Utils) -->
-    <script src="{{ url_for('static', path='shared/js/api-client.js') }}"></script>
+    <script defer src="{{ url_for('static', path='shared/js/api-client.js') }}"></script>
 
     <!-- 6. SIXTH: Alpine.js v3 with CDN fallback (with defer) -->
     <script>