feat: settings panel with Cmd+, shortcut (macOS standard)

- Full settings page as modal overlay (blur backdrop)
- Opens via gear icon on connect/call screens or Cmd+, (Ctrl+, on Win/Linux)
- Escape or click outside to close
- Settings: relay, room, alias, OS AEC toggle, AGC toggle
- Identity section showing fingerprint and identity file path
- Recent rooms management (remove individual, clear all)
- Save syncs back to connect form
- Gear icon on both connect and in-call screens

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

desktop/src/style.css

@@ -342,3 +342,164 @@ button.primary:disabled { opacity: 0.5; cursor: not-allowed; }
   font-family: monospace;
   padding: 4px;
 }
+
+/* ── Icon button ── */
+.icon-btn {
+  background: none;
+  border: 1px solid #444;
+  border-radius: 8px;
+  color: var(--text-dim);
+  font-size: 18px;
+  width: 36px;
+  height: 36px;
+  cursor: pointer;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  transition: all 0.15s;
+}
+
+.icon-btn:hover { border-color: var(--accent); color: var(--text); }
+.icon-btn.small { width: 28px; height: 28px; font-size: 14px; }
+
+.call-header-row {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  gap: 8px;
+}
+
+/* ── Settings panel ── */
+#settings-panel {
+  position: fixed;
+  inset: 0;
+  background: rgba(0, 0, 0, 0.6);
+  backdrop-filter: blur(4px);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  z-index: 100;
+  padding: 20px;
+}
+
+.settings-card {
+  background: var(--bg);
+  border: 1px solid #333;
+  border-radius: 16px;
+  padding: 24px;
+  width: 100%;
+  max-width: 380px;
+  max-height: 90vh;
+  overflow-y: auto;
+  display: flex;
+  flex-direction: column;
+  gap: 20px;
+}
+
+.settings-header {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+}
+
+.settings-header h2 {
+  font-size: 18px;
+  font-weight: 600;
+}
+
+.settings-section {
+  display: flex;
+  flex-direction: column;
+  gap: 10px;
+}
+
+.settings-section h3 {
+  font-size: 12px;
+  text-transform: uppercase;
+  letter-spacing: 1px;
+  color: var(--text-dim);
+  border-bottom: 1px solid #333;
+  padding-bottom: 4px;
+}
+
+.settings-section label {
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+  font-size: 11px;
+  color: var(--text-dim);
+  text-transform: uppercase;
+  letter-spacing: 0.5px;
+}
+
+.settings-section input[type="text"] {
+  background: var(--surface);
+  border: 1px solid #333;
+  border-radius: 8px;
+  padding: 8px 10px;
+  color: var(--text);
+  font-size: 14px;
+  outline: none;
+}
+
+.settings-section input[type="text"]:focus {
+  border-color: var(--accent);
+}
+
+.setting-row {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  padding: 4px 0;
+}
+
+.setting-label {
+  font-size: 12px;
+  color: var(--text-dim);
+}
+
+.fp-display-large {
+  font-family: monospace;
+  font-size: 12px;
+  color: var(--text);
+  word-break: break-all;
+}
+
+.recent-rooms-list {
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+}
+
+.recent-room-item {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  background: var(--surface);
+  border-radius: 8px;
+  padding: 6px 10px;
+  font-size: 13px;
+}
+
+.recent-room-item .remove {
+  background: none;
+  border: none;
+  color: var(--text-dim);
+  cursor: pointer;
+  font-size: 16px;
+}
+
+.recent-room-item .remove:hover { color: var(--red); }
+
+.secondary-btn {
+  background: var(--surface);
+  border: 1px solid #444;
+  border-radius: 8px;
+  padding: 8px;
+  color: var(--text-dim);
+  font-size: 13px;
+  cursor: pointer;
+  transition: all 0.15s;
+}
+
+.secondary-btn:hover { border-color: var(--accent); color: var(--text); }