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/plugins/tests/board-find-replace.test.js

@@ -76,11 +76,16 @@ describe('Search: Find/Replace', () => {
         if (dialog?.classList.contains('open')) {
             const okBtn = document.getElementById('dialog-ok');
             if (okBtn) click(okBtn);
-            await sleep(600);
         }
 
-        const updated1 = await getCard(c1.id);
-        const updated2 = await getCard(c2.id);
+        // Poll until the replace has actually persisted
+        let updated1, updated2;
+        for (let i = 0; i < 40; i++) {
+            await sleep(100);
+            updated1 = await getCard(c1.id);
+            if (updated1?.body === 'goodbye world goodbye') break;
+        }
+        updated2 = await getCard(c2.id);
         expect(updated1.body).toBe('goodbye world goodbye');
         expect(updated2.body).toBe('goodbye there');
     });