SEARCH-1: separator-insensitive NameSearch + OriginBreeder (Herkunft) filter

- Gerbil.NameSearch (lowercase, strip whitespace/.-_) auto-synced in ApplicationContext
  .SaveChanges; Gridify-filterable so 'clan kleine chaoten' matches 'Clan-Kleine-Chaoten'
  (client strips separators the same way). GerbilSearch.Normalize shared helper.
- Gerbil.OriginBreeder (free-text Herkunft) on DTO+Input, set by the FEAT-8 import from the
  source Zucht (imported animals have no OriginContact). Gridify-filterable.
- GET /gerbils/breeders: distinct non-empty OriginBreeder values for the Herkunft dropdown.
- Migration AddSearchFields (+ NameSearch backfill SQL for existing rows).

GerbilManagerWebAPI/Migrations/20260606070015_AddSearchFields.cs

@@ -0,0 +1,44 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace GerbilManagerWebAPI.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddSearchFields : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<string>(
+                name: "NameSearch",
+                table: "Gerbils",
+                type: "text",
+                nullable: true);
+
+            migrationBuilder.AddColumn<string>(
+                name: "OriginBreeder",
+                table: "Gerbils",
+                type: "text",
+                nullable: true);
+
+            // Backfill NameSearch for existing rows (lowercase, strip whitespace/.-_),
+            // matching GerbilSearch.Normalize. New/updated rows stay in sync via
+            // ApplicationContext.SaveChanges.
+            migrationBuilder.Sql(
+                "UPDATE \"Gerbils\" SET \"NameSearch\" = lower(regexp_replace(\"Name\", '[[:space:]._-]', '', 'g'));");
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "NameSearch",
+                table: "Gerbils");
+
+            migrationBuilder.DropColumn(
+                name: "OriginBreeder",
+                table: "Gerbils");
+        }
+    }
+}

GerbilManagerWebAPI/Migrations/ApplicationContextModelSnapshot.cs

@@ -696,9 +696,15 @@ namespace GerbilManagerWebAPI.Migrations
                         .IsRequired()
                         .HasColumnType("text");
 
+                    b.Property<string>("NameSearch")
+                        .HasColumnType("text");
+
                     b.Property<string>("Notes")
                         .HasColumnType("text");
 
+                    b.Property<string>("OriginBreeder")
+                        .HasColumnType("text");
+
                     b.Property<Guid?>("OriginContactId")
                         .HasColumnType("uuid");