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/gallery.test.js

@@ -9,7 +9,7 @@ describe('Gallery', () => {
 
     it('opens on button click', async () => {
         click('#gallery-btn');
-        for (let i = 0; i < 20; i++) {
+        for (let i = 0; i < 40; i++) {
             if ($('#gallery')?.classList.contains('open')) break;
             await sleep(100);
         }
@@ -22,7 +22,7 @@ describe('Gallery', () => {
 
     it('shows image count', async () => {
         click('#gallery-btn');
-        for (let i = 0; i < 20; i++) {
+        for (let i = 0; i < 40; i++) {
             if ($('#gallery')?.classList.contains('open')) break;
             await sleep(100);
         }
@@ -31,7 +31,7 @@ describe('Gallery', () => {
 
     it('closes on close button', async () => {
         click('#gallery-btn');
-        for (let i = 0; i < 20; i++) {
+        for (let i = 0; i < 40; i++) {
             if ($('#gallery')?.classList.contains('open')) break;
             await sleep(100);
         }