electron: external data dir, packaged path fix, footer responsive, test stabilization

- DB + uploads stored outside app bundle (survives updates)
- Router uses DOCUMENT_ROOT instead of __DIR__ (fixes AppImage paths)
- Footer count shifts right below 1250px, min-width 1150px
- Gallery opens gracefully on fetch errors
- Stabilized gallery, export, and find/replace tests with poll loops

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

public/js/modules/gallery.js

@@ -88,11 +88,15 @@ export async function openGallery() {
     // api('api/cards') (not state.cards) guarantees bodies are present
     // — state.cards may still be in the two-phase lazy-load with
     // body=null on most entries.
-    const [files, cards] = await Promise.all([
-        api('api/uploads'),
-        api('api/cards'),
-    ]);
-    galleryCards = cards || [];
+    let files = [], cards = [];
+    try {
+        [files, cards] = await Promise.all([
+            api('api/uploads'),
+            api('api/cards'),
+        ]);
+    } catch {}
+    files = Array.isArray(files) ? files : [];
+    galleryCards = Array.isArray(cards) ? cards : [];
     const referenced = getReferencedUrls();
     const grid = $('gallery-grid');
     const count = $('gallery-count');