fix(voice,knowledge): mic recording + pagination + STT-only mode

Voice: recreate AudioRecorder each session to avoid stale native
state, improve permission handling (re-check after settings), show
feedback after 3 consecutive empty transcripts, allow STT-only mode
when TTS is unavailable.

Knowledge: hydrate IDs immediately after loading more pages so
scroll-based pagination doesn't stall at the bottom.

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

lib/data/api/voice_api.dart

@@ -15,8 +15,9 @@ class VoiceStatus {
     required this.tts,
   });
 
-  /// True only when voice is enabled AND both STT and TTS are ready.
-  bool get fullyAvailable => enabled && stt && tts;
+  /// True when voice is enabled and at least STT is ready.
+  /// TTS is optional — voice mode works without it (STT-only).
+  bool get fullyAvailable => enabled && stt;
 
   factory VoiceStatus.fromJson(Map<String, dynamic> json) => VoiceStatus(
         enabled: json['enabled'] as bool? ?? false,