feat(voice): add VoiceNotifier with recording, silence detection, and streaming TTS

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

test/widget_test.dart

@@ -1,4 +1,5 @@
 import 'package:fabled_app/data/api/voice_api.dart';
+import 'package:fabled_app/providers/voice_provider.dart';
 import 'package:fabled_app/data/models/knowledge_item.dart';
 import 'package:fabled_app/data/models/note.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -98,4 +99,51 @@ void main() {
       expect(status.fullyAvailable, isFalse);
     });
   });
+
+  group('VoiceNotifier sentence extraction', () {
+    test('extracts complete sentences at full stops', () {
+      final result = extractSentences('Hello world. How are you? I am fine!');
+      expect(result.sentences,
+          equals(['Hello world.', 'How are you?', 'I am fine!']));
+      expect(result.remainder, equals(''));
+    });
+
+    test('leaves incomplete fragment in remainder', () {
+      final result = extractSentences('Hello world. Incomplete');
+      expect(result.sentences, equals(['Hello world.']));
+      expect(result.remainder, equals('Incomplete'));
+    });
+
+    test('returns empty sentences and full text when no boundary', () {
+      final result = extractSentences('No boundary here');
+      expect(result.sentences, isEmpty);
+      expect(result.remainder, equals('No boundary here'));
+    });
+  });
+
+  group('VoiceNotifier markdown stripping', () {
+    test('strips code fences', () {
+      expect(stripMarkdownForTts('Before\n```dart\ncode\n```\nAfter'),
+          equals('Before After'));
+    });
+
+    test('strips bold and italic markers', () {
+      expect(stripMarkdownForTts('**bold** and *italic*'),
+          equals('bold and italic'));
+    });
+
+    test('strips headers', () {
+      expect(stripMarkdownForTts('## Section title'), equals('Section title'));
+    });
+
+    test('keeps link text, removes URL', () {
+      expect(stripMarkdownForTts('[click here](https://example.com)'),
+          equals('click here'));
+    });
+
+    test('strips list markers', () {
+      expect(stripMarkdownForTts('- item one\n- item two'),
+          equals('item one item two'));
+    });
+  });
 }