fix(map): theme fullscreen button with accent colour

Replace plain white with --color-accent/--color-accent-on so the button
reads as a site control rather than a stray MapLibre element.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Vgmzx8VTTTmCskSpQtsLTr

themes/intotheeast/css/style.css

@@ -669,10 +669,10 @@ body::after {
     right: var(--space-2);
     width: 2rem;
     height: 2rem;
-    background: rgba(255, 255, 255, 0.9);
+    background: var(--color-accent);
     border: none;
     border-radius: var(--radius-sm);
-    color: var(--color-ink);
+    color: var(--color-accent-on);
     cursor: pointer;
     display: flex;
     align-items: center;
@@ -682,7 +682,7 @@ body::after {
     transition: background 0.15s;
 }
 
-.feed-map-fullscreen-btn:hover { background: rgba(255, 255, 255, 1); }
+.feed-map-fullscreen-btn:hover { background: var(--color-accent-hover); }
 
 .feed-map-fs-close { display: none; font-size: 1rem; line-height: 1; }