feat(map): mobile fullscreen button for feed mini-map

Button in the bottom-right corner of the map, hidden ≥769px. Clicking
it toggles .is-fullscreen on .feed-map-wrap (position:fixed, full
viewport), locks body scroll, and calls feedMap.resize() so MapLibre
re-renders at the new size. Icon swaps between expand SVG and ✕.

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

themes/intotheeast/css/style.css

@@ -653,6 +653,7 @@ body::after {
 }
 
 .feed-map {
+    position: relative;
     height: 240px;
     width: 100%;
 }
@@ -661,6 +662,51 @@ body::after {
     .feed-map { height: 300px; }
 }
 
+.feed-map-fullscreen-btn {
+    position: absolute;
+    bottom: var(--space-2);
+    right: var(--space-2);
+    width: 2rem;
+    height: 2rem;
+    background: rgba(255, 255, 255, 0.9);
+    border: none;
+    border-radius: var(--radius-sm);
+    color: var(--color-ink);
+    cursor: pointer;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    z-index: 20;
+    box-shadow: var(--shadow-sm);
+    transition: background 0.15s;
+}
+
+.feed-map-fullscreen-btn:hover { background: rgba(255, 255, 255, 1); }
+
+.feed-map-fs-close { display: none; font-size: 1rem; line-height: 1; }
+
+@media (min-width: 769px) {
+    .feed-map-fullscreen-btn { display: none; }
+}
+
+.feed-map-wrap.is-fullscreen {
+    position: fixed;
+    inset: 0;
+    z-index: 9999;
+    margin: 0;
+    border-radius: 0;
+    border: none;
+}
+
+.feed-map-wrap.is-fullscreen .feed-map {
+    height: 100dvh;
+}
+
+.feed-map-wrap.is-fullscreen .feed-map-link { display: none; }
+
+.feed-map-wrap.is-fullscreen .feed-map-fs-open { display: none; }
+.feed-map-wrap.is-fullscreen .feed-map-fs-close { display: block; }
+
 .feed-map-link {
     display: block;
     text-align: right;