fix: prevent duplicate partnumbers in stock mappings table

Add duplicate detection before batch insert of auto-mappings:
- Query existing partnumbers from lot_partnumbers table
- Build case-insensitive set of existing entries
- Filter out duplicates before CreateInBatches
- Also prevent duplicates within single batch

This ensures partnumber uniqueness as primary key requires.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

internal/lotmatch_old/resolver_test.go

@@ -0,0 +1,62 @@
+package lotmatch
+
+import (
+	"testing"
+
+	"git.mchus.pro/mchus/priceforge/internal/models"
+)
+
+func TestLotResolverPrecedence(t *testing.T) {
+	resolver := NewLotResolver(
+		[]models.LotPartnumber{
+			{Partnumber: "PN-1", LotName: "LOT_A"},
+		},
+		[]models.Lot{
+			{LotName: "CPU_X_LONG"},
+			{LotName: "CPU_X"},
+		},
+	)
+
+	lot, by, err := resolver.Resolve("PN-1")
+	if err != nil || lot != "LOT_A" || by != "mapping_table" {
+		t.Fatalf("expected mapping_table LOT_A, got lot=%s by=%s err=%v", lot, by, err)
+	}
+
+	lot, by, err = resolver.Resolve("CPU_X")
+	if err != nil || lot != "CPU_X" || by != "article_exact" {
+		t.Fatalf("expected article_exact CPU_X, got lot=%s by=%s err=%v", lot, by, err)
+	}
+
+	lot, by, err = resolver.Resolve("CPU_X_LONG_001")
+	if err != nil || lot != "CPU_X_LONG" || by != "prefix" {
+		t.Fatalf("expected prefix CPU_X_LONG, got lot=%s by=%s err=%v", lot, by, err)
+	}
+}
+
+func TestMappingMatcherWildcardAndExactLot(t *testing.T) {
+	matcher := NewMappingMatcher(
+		[]models.LotPartnumber{
+			{Partnumber: "R750*", LotName: "SERVER_R750"},
+			{Partnumber: "HDD-01", LotName: "HDD_01"},
+		},
+		[]models.Lot{
+			{LotName: "MEM_DDR5_16G_4800"},
+		},
+	)
+
+	check := func(partnumber string, want string) {
+		t.Helper()
+		got := matcher.MatchLots(partnumber)
+		if len(got) != 1 || got[0] != want {
+			t.Fatalf("partnumber %s: expected [%s], got %#v", partnumber, want, got)
+		}
+	}
+
+	check("R750XD", "SERVER_R750")
+	check("HDD-01", "HDD_01")
+	check("MEM_DDR5_16G_4800", "MEM_DDR5_16G_4800")
+
+	if got := matcher.MatchLots("UNKNOWN"); len(got) != 0 {
+		t.Fatalf("expected no matches for UNKNOWN, got %#v", got)
+	}
+}