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/shared/macros/charts.html

@@ -5,7 +5,7 @@
 
   Prerequisites:
     Add Chart.js CDN to your base template:
-    <script src="https://cdn.jsdelivr.net/npm/chart.js@4.4.1/dist/chart.umd.min.js"></script>
+    <script defer src="https://cdn.jsdelivr.net/npm/chart.js@4.4.1/dist/chart.umd.min.js"></script>
 
   Usage:
     {% from 'shared/macros/charts.html' import chart_card, line_chart, bar_chart, doughnut_chart %}