Add stable share fingerprints and near-match conflict routing

lib/features/local/local_models.dart

@@ -335,12 +335,14 @@ class SourceProfileLink {
     required this.lastSeenAt,
     this.sourceUserId,
     this.sourceThreadId,
+    this.sourceFingerprint,
   });
 
   final String id;
   final String sourceApp;
   final String? sourceUserId;
   final String? sourceThreadId;
+  final String? sourceFingerprint;
   final String normalizedDisplayName;
   final String profileId;
   final DateTime firstSeenAt;
@@ -351,6 +353,7 @@ class SourceProfileLink {
     String? sourceApp,
     String? sourceUserId,
     String? sourceThreadId,
+    String? sourceFingerprint,
     String? normalizedDisplayName,
     String? profileId,
     DateTime? firstSeenAt,
@@ -361,6 +364,7 @@ class SourceProfileLink {
       sourceApp: sourceApp ?? this.sourceApp,
       sourceUserId: sourceUserId ?? this.sourceUserId,
       sourceThreadId: sourceThreadId ?? this.sourceThreadId,
+      sourceFingerprint: sourceFingerprint ?? this.sourceFingerprint,
       normalizedDisplayName:
           normalizedDisplayName ?? this.normalizedDisplayName,
       profileId: profileId ?? this.profileId,
@@ -375,6 +379,7 @@ class SourceProfileLink {
       'sourceApp': sourceApp,
       'sourceUserId': sourceUserId,
       'sourceThreadId': sourceThreadId,
+      'sourceFingerprint': sourceFingerprint,
       'normalizedDisplayName': normalizedDisplayName,
       'profileId': profileId,
       'firstSeenAt': firstSeenAt.toUtc().toIso8601String(),
@@ -388,6 +393,7 @@ class SourceProfileLink {
       sourceApp: json['sourceApp'] as String,
       sourceUserId: json['sourceUserId'] as String?,
       sourceThreadId: json['sourceThreadId'] as String?,
+      sourceFingerprint: json['sourceFingerprint'] as String?,
       normalizedDisplayName: json['normalizedDisplayName'] as String? ?? '',
       profileId: json['profileId'] as String,
       firstSeenAt: DateTime.parse(json['firstSeenAt'] as String).toLocal(),
@@ -480,7 +486,11 @@ class SharedMessageEntry {
   }
 }
 
-enum SharedInboxReason { ambiguousProfileMatch, missingIdentity }
+enum SharedInboxReason {
+  ambiguousProfileMatch,
+  nearProfileConflict,
+  missingIdentity,
+}
 
 @immutable
 class SharedInboxEntry {
@@ -493,6 +503,7 @@ class SharedInboxEntry {
     required this.reason,
     required this.candidateProfileIds,
     required this.normalizedDisplayName,
+    this.sourceFingerprint,
     this.sourceDisplayName,
     this.sourceUserId,
     this.sourceThreadId,
@@ -506,6 +517,7 @@ class SharedInboxEntry {
   final SharedInboxReason reason;
   final List<String> candidateProfileIds;
   final String normalizedDisplayName;
+  final String? sourceFingerprint;
   final String? sourceDisplayName;
   final String? sourceUserId;
   final String? sourceThreadId;
@@ -519,6 +531,7 @@ class SharedInboxEntry {
     SharedInboxReason? reason,
     List<String>? candidateProfileIds,
     String? normalizedDisplayName,
+    String? sourceFingerprint,
     String? sourceDisplayName,
     String? sourceUserId,
     String? sourceThreadId,
@@ -533,6 +546,7 @@ class SharedInboxEntry {
       candidateProfileIds: candidateProfileIds ?? this.candidateProfileIds,
       normalizedDisplayName:
           normalizedDisplayName ?? this.normalizedDisplayName,
+      sourceFingerprint: sourceFingerprint ?? this.sourceFingerprint,
       sourceDisplayName: sourceDisplayName ?? this.sourceDisplayName,
       sourceUserId: sourceUserId ?? this.sourceUserId,
       sourceThreadId: sourceThreadId ?? this.sourceThreadId,
@@ -549,6 +563,7 @@ class SharedInboxEntry {
       'reason': reason.name,
       'candidateProfileIds': candidateProfileIds,
       'normalizedDisplayName': normalizedDisplayName,
+      'sourceFingerprint': sourceFingerprint,
       'sourceDisplayName': sourceDisplayName,
       'sourceUserId': sourceUserId,
       'sourceThreadId': sourceThreadId,
@@ -573,6 +588,7 @@ class SharedInboxEntry {
               .map((dynamic id) => '$id')
               .toList(growable: false),
       normalizedDisplayName: json['normalizedDisplayName'] as String? ?? '',
+      sourceFingerprint: json['sourceFingerprint'] as String?,
       sourceDisplayName: json['sourceDisplayName'] as String?,
       sourceUserId: json['sourceUserId'] as String?,
       sourceThreadId: json['sourceThreadId'] as String?,