feat: Fehler-melden + Datenherkunft auf Kontakte & Würfe erweitern

- Kontakt-Detailseite: „Fehler melden"- und „Datenherkunft"-Button.
- Wurf-Ansicht: „Datenherkunft"-Button (Feedback war bereits vorhanden).
- Feedback-Entity um loses, nullable ContactId erweitert (kein FK → übersteht
  Ingest-Wipe); Migration AddFeedbackContactId.
- Contact.Provenance + Litter.Provenance (nullable text); Migration
  AddContactLitterProvenance; im Ingest gemappt und in den DTOs zurückgegeben.
- Import: build_entity_provenance() generalisiert; Kontakte (sourceFiles,
  Züchter/Abnehmer-Hinweise) und Würfe (Wurfchronik vs. Diagramm-rekonstruiert,
  Geschwister-Merge) erhalten Herkunftsdaten in resolved_import.json.
- Frontend: ProvenanceDialog generalisiert (EntityProvenance + entityLabel).

Tests erweitert (Ingest-Round-trip Kontakt/Wurf, contact-scoped Feedback
übersteht Wipe). dotnet(212)/vitest(129)/playwright(36)/tsc/eslint grün.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

GerbilManagerWebAPI/Migrations/20260622135306_AddFeedbackContactId.cs

@@ -0,0 +1,29 @@
+using System;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace GerbilManagerWebAPI.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddFeedbackContactId : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<Guid>(
+                name: "ContactId",
+                table: "Feedback",
+                type: "uuid",
+                nullable: true);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "ContactId",
+                table: "Feedback");
+        }
+    }
+}

GerbilManagerWebAPI/Migrations/20260622135338_AddContactLitterProvenance.cs

@@ -0,0 +1,38 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace GerbilManagerWebAPI.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddContactLitterProvenance : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<string>(
+                name: "Provenance",
+                table: "Litters",
+                type: "text",
+                nullable: true);
+
+            migrationBuilder.AddColumn<string>(
+                name: "Provenance",
+                table: "Contacts",
+                type: "text",
+                nullable: true);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "Provenance",
+                table: "Litters");
+
+            migrationBuilder.DropColumn(
+                name: "Provenance",
+                table: "Contacts");
+        }
+    }
+}

GerbilManagerWebAPI/Migrations/ApplicationContextModelSnapshot.cs

@@ -741,6 +741,9 @@ namespace GerbilManagerWebAPI.Migrations
                     b.Property<string>("Phone")
                         .HasColumnType("text");
 
+                    b.Property<string>("Provenance")
+                        .HasColumnType("text");
+
                     b.HasKey("Id");
 
                     b.ToTable("Contacts");
@@ -802,6 +805,9 @@ namespace GerbilManagerWebAPI.Migrations
                     b.Property<DateTimeOffset?>("ClientTimestamp")
                         .HasColumnType("timestamp with time zone");
 
+                    b.Property<Guid?>("ContactId")
+                        .HasColumnType("uuid");
+
                     b.Property<string>("Context")
                         .IsRequired()
                         .HasColumnType("text");
@@ -1046,6 +1052,9 @@ namespace GerbilManagerWebAPI.Migrations
                     b.Property<string>("PairingCode")
                         .HasColumnType("text");
 
+                    b.Property<string>("Provenance")
+                        .HasColumnType("text");
+
                     b.Property<int?>("TotalBorn")
                         .HasColumnType("integer");