feat: add local-first private AI digest workflow

Migrate app code into canonical feature slices, add phone-only AI digest scheduling and review, wire local notification/background task support, and cover the flow with tests.

lib/features/share_intake/domain/signal_share_parser.dart

@@ -0,0 +1,72 @@
+class SignalSharePayload {
+  const SignalSharePayload({
+    required this.messageText,
+    this.sourceDisplayName,
+    this.sourceUserId,
+    this.sourceThreadId,
+  });
+
+  final String messageText;
+  final String? sourceDisplayName;
+  final String? sourceUserId;
+  final String? sourceThreadId;
+}
+
+/// Parses raw shared text from Signal into normalized sender/message fields.
+class SignalShareParser {
+  const SignalShareParser._();
+
+  static final RegExp _namePrefixPattern = RegExp(
+    r'^([^:\n]{2,80}):\s*(.+)$',
+    dotAll: true,
+  );
+
+  static SignalSharePayload parse(String raw) {
+    final String input = raw.trim();
+    if (input.isEmpty) {
+      return const SignalSharePayload(messageText: '');
+    }
+
+    final RegExpMatch? match = _namePrefixPattern.firstMatch(input);
+    if (match == null) {
+      return SignalSharePayload(messageText: input);
+    }
+
+    final String? senderName = _cleanSender(match.group(1));
+    final String messageText = match.group(2)?.trim() ?? input;
+    return SignalSharePayload(
+      messageText: messageText,
+      sourceDisplayName: senderName,
+      sourceUserId: _normalizedKey(senderName),
+      sourceThreadId: null,
+    );
+  }
+
+  static bool looksLikeSignalMessage(String raw) {
+    final String input = raw.trim();
+    if (input.isEmpty) {
+      return false;
+    }
+    return _namePrefixPattern.hasMatch(input);
+  }
+
+  static String? _cleanSender(String? input) {
+    if (input == null) {
+      return null;
+    }
+    final String cleaned = input.trim();
+    return cleaned.isEmpty ? null : cleaned;
+  }
+
+  static String? _normalizedKey(String? input) {
+    if (input == null) {
+      return null;
+    }
+    final String key = input
+        .toLowerCase()
+        .replaceAll(RegExp(r'[^a-z0-9]+'), ' ')
+        .trim()
+        .replaceAll(RegExp(r'\s+'), ' ');
+    return key.isEmpty ? null : 'signal:$key';
+  }
+}