addrkit: strict ordinal matching, LLM-variant guard, externalized prompt

- match: require candidate ordinal to equal the query ordinal in fuzzy search
  (deterministic typo recall 73% -> 80%, no wrong houses)
- resolver: compatibleVariant guard — LLM may only fix street spelling, keeping
  the same words, ordinal and house unit; damerau distance for transpositions
- llm: prompt moved out of code (go:embed default_prompt.txt) with
  llm.system_prompt / llm.system_prompt_file overrides; guided JSON parsing
  tolerant of thinking blocks
- address: recognize ordinals appearing after the street name
- tests: first coverage for the LLM adapter and config prompt loading; README

Measured (sample 200): deterministic 94.7-95.8% exact / 0 wrong across 4 seeds;
LLM+guard typo 90.7-89.8% / 0 wrong. LLM fallback latency ~1.2-1.9s.

internal/domain/match/resolver_test.go

@@ -0,0 +1,52 @@
+package match
+
+import (
+	"testing"
+
+	"git.totmin.ru/en2zmax/addrkit/internal/domain/address"
+)
+
+// TestCompatibleVariant encodes the safety contract for LLM rewrites: only a
+// spelling fix of the same street, with the same ordinal and house unit, may be
+// considered.
+func TestCompatibleVariant(t *testing.T) {
+	orig := address.Parse("2-я Сухарная улица 95")
+	tests := []struct {
+		name    string
+		variant string
+		want    bool
+	}{
+		{"spelling fix (transposition)", "2-я Сухраная улица 95", true},
+		{"reordered words", "Сухарная 2-я улица 95", true},
+		{"ordinal dropped", "Сухарная улица 95", false},
+		{"different street", "Королева улица 95", false},
+		{"house changed", "2-я Сухарная улица 96", false},
+		{"building added", "2-я Сухарная улица 95 к1", false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := compatibleVariant(orig, address.Parse(tt.variant))
+			if got != tt.want {
+				t.Errorf("compatibleVariant(%q) = %v, want %v", tt.variant, got, tt.want)
+			}
+		})
+	}
+}
+
+// TestCompatibleVariantProtectsApartment ensures "кв 5" is not folded into a
+// corpus "к5" by the model.
+func TestCompatibleVariantProtectsApartment(t *testing.T) {
+	orig := address.Parse("ул. Елоховская, д. 43 кв. 5")
+	if compatibleVariant(orig, address.Parse("ул. Елоховская 43 к5")) {
+		t.Fatal("apartment must not be rewritten as a corpus")
+	}
+}
+
+func TestDamerau(t *testing.T) {
+	if got := damerau("гоглоя", "гоголя"); got != 1 {
+		t.Errorf("transposition distance = %d, want 1", got)
+	}
+	if got := damerau("сееврный", "северная"); got < 2 {
+		t.Errorf("expected a larger distance for a different word, got %d", got)
+	}
+}