OWNERSHIP: residency classification (Bestand vs external ancestors)

Per hive/agents/god/OWNERSHIP-residency.md (Julian): "Clan kleine Chaoten"
is the wife's own Zucht. Classify each animal:
 (a) RESIDENT if zuchtCanon contains 'kleinechaote' (separator/declension-
     insensitive: "v.d. Kleinen Chaoten", "Clan-Kleine-Chaoten", …); OR
 (b) PARENT EXCEPTION — a parent of a Clan offspring is resident even if its
     own Zuchtname is foreign (you can only breed a Clan litter if the parents
     were in your care). Runs AFTER the parentRefs→litter linking.
Otherwise EXTERNAL (pedigree ancestor, not living stock — kept, not deleted).

Stored as a dedicated Gerbil.IsResident bool (distinct from Status/Abgabe —
origin/identity, not current location), defaulting true (own stock unless
marked external; DB HasDefaultValue(true)). Additive migration
AddGerbilResidency; has-pending-model-changes clean. Round-trips in
GerbilDto/GerbilInput and is Gridify-filterable (isResident==true) so Kevin
can build a "nur Bestand" filter. ImportService computes it at (re-)import
and refreshes existing rows on the idempotent sweep. ResidencySummary added
to the import report.

Projected on real data: 306 loadable → 227 resident (188 rule a, +39 via
parent exception), 79 external ancestors.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

GerbilManagerWebAPI/Migrations/20260606085655_AddGerbilResidency.cs

@@ -0,0 +1,29 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace GerbilManagerWebAPI.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddGerbilResidency : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<bool>(
+                name: "IsResident",
+                table: "Gerbils",
+                type: "boolean",
+                nullable: false,
+                defaultValue: true);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "IsResident",
+                table: "Gerbils");
+        }
+    }
+}