FEAT-8c: import loader — /import/dry-run + /import/execute (gated)

- Additive migration: Gerbil.RawImportData + Litter.PairingCode (Zuchtnummer der Verpaarung).
- ImportService consumes tools/import/output (animals.json + litters.json): litters first
  (authoritative), then conflict-free animals with a DOB; high-confidence (hoch) litter links
  set LitterId, date-only/ambiguous links quarantined; conflicts + stubs never loaded.
  Genotype mapped8locus -> frozen compact string; rawGenotype+unmappedTokens preserved in
  RawImportData; Farbschlag matched to ColorVariety; gender inferred from litter role;
  provenance ImportSource/ExternalRef; idempotent (ExternalRef / Name+Date). Photos copied to store.
- ImportEndpoints: POST /import/dry-run (no writes, Julian-readable report) + /import/execute (gated).

GerbilManagerWebAPI/Migrations/ApplicationContextModelSnapshot.cs

@@ -650,6 +650,9 @@ namespace GerbilManagerWebAPI.Migrations
                     b.Property<Guid?>("OriginContactId")
                         .HasColumnType("uuid");
 
+                    b.Property<string>("RawImportData")
+                        .HasColumnType("text");
+
                     b.Property<Guid?>("ReceiverContactId")
                         .HasColumnType("uuid");
 
@@ -759,6 +762,9 @@ namespace GerbilManagerWebAPI.Migrations
                     b.Property<string>("Notes")
                         .HasColumnType("text");
 
+                    b.Property<string>("PairingCode")
+                        .HasColumnType("text");
+
                     b.Property<int?>("TotalBorn")
                         .HasColumnType("integer");