feat(android): add Android release workflow and shuffle UI improvements

Adds a new Android release workflow to sign and publish APKs when tags are pushed. Also enhances wallpaper shuffle by tracking seen IDs to reduce repeats. UI changes in App.tsx introduce lazy loading for the gallery and improved navigation/history handling.

- Add Android signing workflow with keystore secrets
- Track shuffle seen IDs to avoid image repeats
- Enable gallery lazy loading via sentinel and observer

src/styles.css

@@ -149,6 +149,7 @@ nav svg { width: 21px; }
 .gallery-empty p { max-width: 290px; margin: 8px 0 2px; font-size: 13px; line-height: 1.5; }
 .gallery-empty .primary { max-width: 260px; }
 .gallery-status { padding: 28px 0; text-align: center; color: #6d776f; font-size: 13px; }
+.gallery-load-sentinel { height: 1px; }
 .load-more { width: 100%; height: 48px; margin-top: 18px; border: 1px solid #b9c8bb; border-radius: 15px; color: var(--green); background: white; font-weight: 750; }
 .save-crop { background: var(--green); color: white; }
 .crop-editor { padding-bottom: max(28px, env(safe-area-inset-bottom)); }