Optimize: drop Bootstrap CDN, add caching headers & image hints

Performance / self-hosting
- Remove the render-blocking Bootstrap 4 CDN stylesheet (~160 KB + extra
  DNS/TLS to a third party) and replace it with ~60 lines of self-hosted
  grid/utility CSS covering the small subset actually used (container, row,
  col-lg-5/6/7, order-lg, align-items-center, text-center, table-responsive,
  spacing, and the button base). Verified across desktop/tablet/mobile.
- Add a Cloudflare Pages `_headers` file: 30-day cache for static media and
  icons, 1-day for css/js, plus baseline security headers
  (X-Content-Type-Options, Referrer-Policy).
- Add decoding="async" to all lazily-loaded images.

The site now loads no third-party CSS; only Google Fonts remain external.
SCSS source kept in sync (new components/_grid partial; button base + reset
mirrored in main.scss).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

css/main.scss

@@ -22,9 +22,19 @@ $l-break: 1199px;
 
 * { box-sizing: border-box; }
 
+@import 'components/grid';
+
 //btns
 .btn {
   @include Libre;
+  display: inline-block;
+  vertical-align: middle;
+  text-align: center;
+  border: 1px solid transparent;
+  line-height: 1.5;
+  cursor: pointer;
+  text-decoration: none;
+  user-select: none;
   font-size: 14px;
   letter-spacing: 0.3px;
   padding: 0.55rem 1.5rem;
@@ -33,10 +43,19 @@ $l-break: 1199px;
   & + .btn { margin-left: 0.5rem; }
 }
 
+.btn-light {
+  color: #212529;
+  background-color: #f8f9fa;
+  border-color: #f8f9fa;
+}
+
 .btn-primary {
+  color: $white;
   background-color: $gold;
   border-color: $gold;
 
+  &:hover { color: $white; }
+
   &:hover {
     background-color: darken($gold, 10%);
     border-color: darken($gold, 10%);
@@ -73,9 +92,12 @@ p, a, li, span, div, td, th {
 
 h1, h2, h3, h4, h5, h6 {
   @include Libre;
+  margin-top: 0;
 }
 
-img { max-width: 100%; }
+p { margin-top: 0; margin-bottom: 1rem; }
+
+img { max-width: 100%; vertical-align: middle; }
 
 .page-content {
   padding-top: 92px;