Revert to static JS site (Svelte built, but no CSR); Optimize images

src/lib/components/SiteHeader.svelte

@@ -1,9 +1,9 @@
 <script lang="ts">
-    import { theme } from '$lib/stores/theme.svelte.js';
-
-    const toggleTheme = () => {
-        theme.set(theme.get() === 'light' ? 'dark' : 'light');
-    };
+    interface Props {
+        /** Caption for the tour video (used by script.js for lightbox); from media data */
+        tourCaption?: string;
+    }
+    let { tourCaption }: Props = $props();
 </script>
 
 <header class="site-header">
@@ -13,6 +13,9 @@
             id="show_video"
             class="emoji-button"
             aria-label="Show video tour"
+            data-name="tour"
+            data-type="video"
+            data-caption={tourCaption}
         >
             🎥
         </button>
@@ -20,7 +23,6 @@
             id="theme-toggle"
             class="emoji-button"
             aria-label="Toggle light/dark theme"
-            onclick={toggleTheme}
         >
             🌓
         </button>