fix(page): improve loading glow visibility, lifecycle, and background fade-in
- Make loading glow more prominent: brighter colors, wider border/outline,
faster 1.5s pulse cycle
- Add background fade-in animation so webview shows white bg immediately
while loading instead of being transparent
- Add did-start-loading handler to re-apply loading class on navigation
- Add did-stop-loading fallback to ensure glow stops if dom-ready doesn't fire
- Transition ready state uses transparent border/outline for smooth fade-out
- Sequence: fade in background (0.3s) → start glow pulse → page loads → end glow