feat(ui,ios): replace audio_router with audio_session + custom VoIP-style picker

User reported: the 'output device' picker only listed AirPlay
destinations (other iPhones / AirPlay speakers / AppleTV) and not
the speaker / iPhone receiver / AirPods / wired headset choices.

Root cause: audio_router 1.1.1's iOS path uses AVRoutePickerView,
which is Apple's **AirPlay** picker UI \u2014 by design it only lists
AirPlay-eligible output destinations, NOT the input/output route
choices we need (speaker vs receiver vs Bluetooth HFP vs wired).
AVRoutePickerView is the right UI for 'cast audio elsewhere'; for
'pick how I hear / talk' (VoIP) the right primitive is direct
AVAudioSession calls.

Fix: replace audio_router with audio_session 0.2.3 (Ryan Heise,
verified publisher, 865k downloads, MIT). audio_session exposes:

  * AVAudioSession.availableInputs \u2014 enumerate every real input
    port: builtInMic, bluetoothHfp, bluetoothA2dp, headsetMic
    (wired), usbAudio, carAudio, airPlay.
  * AVAudioSession.currentRoute \u2014 .inputs + .outputs of the
    active route.
  * AVAudioSession.setPreferredInput(port) \u2014 switch the input
    (HFP / wired / USB / car audio also move output to themselves).
  * AVAudioSession.overrideOutputAudioPort(.speaker | .none) \u2014
    toggle built-in speakerphone vs receiver/earpiece.
  * AVAudioSession.routeChangeStream \u2014 live notifications when
    the user plugs / unplugs / connects a device while the picker
    is open.

This is exactly the same primitive Discord, WhatsApp, FaceTime
use for their VoIP audio chooser. No native UI plugin needed.

New widgets in voice_compact.dart:

  * _AudioOutputTile: shows the active output port name (Speaker /
    iPhone / AirPods / 'Phil's Wired Headset' / etc.) with the
    matching icon. Subscribes to routeChangeStream for live
    updates. Tap opens _AudioOutputPickerSheet.

  * _AudioOutputPickerSheet: bottom sheet with 'Choose audio' title
    and a Discord-style list:
      - Speaker          (volume_up)
      - iPhone           (phone_in_talk; the receiver/earpiece)
      - <BT name>        (bluetooth_audio)
      - <Wired headset>  (headset)
      - <USB / Car>      (usb / directions_car)
    Selected row is highlighted + has a check mark. Tap routes:
      - Speaker  -> overrideOutputAudioPort(.speaker)
      - iPhone   -> overrideOutputAudioPort(.none) + setPreferredInput(builtInMic)
      - External -> overrideOutputAudioPort(.none) + setPreferredInput(port)

  * _PickerRow: shared row widget with selected/check styling.

AppDelegate.swift is unchanged: the manual AVAudioSession
.setCategory(playAndRecord / .voiceChat) we already do at launch
(0466000 / 4ee2b38) is fully compatible with audio_session \u2014 the
plugin only adds Dart-side accessors over the same underlying
AVAudioSession singleton.

Removed l10n keys not used anymore (audioRouteUsb was already gone).
Kept audioRouteSpeaker / Receiver / Bluetooth / WiredHeadset /
CarAudio / Airplay / Unknown \u2014 all still used by the new picker.

flutter analyze: 6 pre-existing Radio deprecation infos (unchanged).
flutter build ios --release --no-codesign: 54.9 s, Runner.app
30.4 MB (+200 KB vs audio_router build).

apps/chanora_flutter/pubspec.yaml

@@ -41,20 +41,28 @@ dependencies:
   freezed_annotation: ^3.1.0
   connectivity_plus: ^6.1.0
   path_provider: ^2.1.4
-  # audio_router 1.1.1 (MIT, supports Android + iOS) drives the
-  # "Audio output" device picker on mobile. iOS displays the native
-  # AVRoutePickerView (AirPlay/Bluetooth/Speaker/Receiver). Android
-  # gets a Material 3 dialog backed by AudioManager.setCommunicationDevice.
-  # No-op on desktop \u2014 we only import the symbols and gate use behind
-  # Platform.isIOS / Platform.isAndroid at the call site.
+  # audio_session 0.2.3 (MIT, Ryan Heise, 865k downloads) gives us
+  # programmatic access to AVAudioSession on iOS + AudioManager on
+  # Android. We use:
   #
-  # Prerequisite the plugin documents: the audio session must be
-  # configured *before* the picker is shown. We already set
-  # AVAudioSession to .playAndRecord/.voiceChat in AppDelegate.swift
-  # (iOS 0466000), so the plugin's iOS path is satisfied. Android
-  # has no audio session yet \u2014 will be addressed when we wire up
-  # the Android target post-rc.8.
-  audio_router: ^1.1.1
+  #   * AVAudioSession.availableInputs \u2014 enumerate real input ports
+  #     (Built-in Mic, Bluetooth HFP, wired headset, USB).
+  #   * AVAudioSession.currentRoute \u2014 inputs + outputs of the
+  #     active route.
+  #   * AVAudioSession.setPreferredInput(port) \u2014 switch input
+  #     (also drives matching output for HFP devices).
+  #   * AVAudioSession.overrideOutputAudioPort(speaker|none) \u2014
+  #     toggle the built-in receiver/earpiece vs speakerphone.
+  #   * AVAudioSession.routeChangeStream \u2014 live notifications when
+  #     the user plugs / unplugs / connects a device.
+  #
+  # This is the right primitive for a VoIP-style 'pick speaker /
+  # receiver / AirPods / wired' picker. Discord, WhatsApp, FaceTime
+  # all do exactly this. We previously tried audio_router 1.1.1
+  # whose iOS path is AVRoutePickerView (the AirPlay button) \u2014 the
+  # wrong UI: only lists AirPlay output destinations, not the
+  # speaker/receiver/Bluetooth choices we actually want.
+  audio_session: ^0.2.3
 
 dev_dependencies:
   flutter_test: