feat(ios,p0): iOS P0 platform, audio fixes, channel UX

apps/chanora_flutter/lib/l10n/app_en.arb

@@ -52,6 +52,7 @@
   "pttCapabilityExplainGoGlobalWindows": "On Windows, Global PTT is engaged automatically once you bind a key. No additional permission is required.",
   "pttCapabilityExplainGoGlobalMacos": "On macOS, Global PTT requires Input Monitoring permission. Open System Settings → Privacy & Security → Input Monitoring, allow Chanora, then re-bind the key.",
   "pttCapabilityExplainGoGlobalLinux": "On Linux, Global PTT requires a GNOME-Wayland desktop with the GlobalShortcuts portal. Re-bind the key and accept the desktop's shortcut dialog when it appears.",
+  "pttCapabilityExplainGoGlobalIos": "On iOS, Apple does not expose global hotkeys to apps. Chanora uses the on-screen Push-to-Talk button and only transmits while the app is in the foreground.",
   "pttCapabilityExplainGoGlobalGeneric": "Global PTT is not available in this environment. Focused PTT will keep working while the Chanora window has focus.",
   "pttConfigureAction": "Configure",
   "pttConfigureTitle": "Configure Push-to-Talk binding",
@@ -66,6 +67,7 @@
   "outputMuteAction": "Mute speaker",
   "outputUnmuteAction": "Unmute speaker",
   "joinChannelAction": "Join channel",
+  "leaveChannelAction": "Leave channel",
   "channelPasswordTitle": "Channel password",
   "bookmarksHeading": "Bookmarks",
   "bookmarksEmpty": "No bookmarks yet. Enter a server above and tap \"Save bookmark\".",
@@ -140,6 +142,7 @@
   "audioRouteCarAudio": "Car audio",
   "audioRouteAirplay": "AirPlay",
   "audioRouteUnknown": "Unknown",
+  "channelJoinAlreadyIn": "Already in this channel.",
   "channelJoinFailedPermission": "Insufficient permission to join this channel.",
   "channelJoinFailedPassword": "Wrong channel password.",
   "channelJoinFailedFull": "Channel is full.",