feat: fingerprint at startup, relay+room pairs, auto-reconnect, cleanup

#7 Fingerprint shown before connecting — new get_identity command reads
   ~/.wzp/identity at startup (generates if missing). Click to copy.

#8 Recent rooms store (relay, room) pairs — clicking a chip fills both
   fields. Settings panel shows relay alongside room name. Migrates
   old string[] format automatically.

#9 Auto-reconnect on unexpected disconnect — exponential backoff
   (1s, 2s, 4s... max 10s), up to 5 attempts. Yellow blinking dot
   shows reconnecting state. Stops if user clicks hangup.

#10 Audio handle cleanup — CPAL handles stored in SyncWrapper (no more
    mem::forget), dropped properly on CallEngine::stop().

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

desktop/src/style.css

@@ -201,6 +201,16 @@ button.primary:disabled { opacity: 0.5; cursor: not-allowed; }
   50% { opacity: 0.4; }
 }
 
+.status-dot.reconnecting {
+  background: var(--yellow);
+  animation: blink 0.5s infinite;
+}
+
+@keyframes blink {
+  0%, 100% { opacity: 1; }
+  50% { opacity: 0.1; }
+}
+
 .call-timer {
   font-size: 14px;
   color: var(--text-dim);