ui: visual polish — animations, icons, and interaction improvements

- Spin animation on ⟳ delivery status during SENDING/ENCRYPTING states
- Pulsing ● dot on PTT LIVE badge (pttLivePulse keyframe)
- Read receipt pill: hover scale/opacity transition, symmetric padding
- PiP resize handles: larger dots (5px), wider hit area (24px), higher contrast
- ForwardMessageDialog: position:relative on scroll container, spinner overlay 0.35 opacity
- Boot sequence: 45ms interval (was 65ms), brighter ESC hint (0.55 opacity)
- Location button: Icons.Pin → Icons.SpaceGlobe (globe icon)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/index.css

@@ -156,6 +156,16 @@ audio:not([controls]) {
   display: none !important;
 }
 
+@keyframes pttLivePulse {
+  0%,
+  100% {
+    opacity: 1;
+  }
+  50% {
+    opacity: 0.25;
+  }
+}
+
 /* Fix Firefox rendering lists that have empty items with those items collapsed in on eachother */
 li p::before {
   content: '';