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/adapters/httpapi/server_test.go

@@ -19,7 +19,7 @@ import (
 func testResolver(t *testing.T) *match.Resolver {
 	t.Helper()
 	var entries []address.Entry
-	for _, a := range []string{"Станционная улица 1/1", "Искитимская улица 5"} {
+	for _, a := range []string{"Станционная улица 1/1", "2-я Станционная улица 1/1", "Искитимская улица 5"} {
 		p := address.Parse(a)
 		entries = append(entries, address.Entry{
 			ID: a, Address: a, District: "Тестовый",
@@ -68,7 +68,7 @@ func TestResolveEndpoint(t *testing.T) {
 	if err := json.NewDecoder(resp.Body).Decode(&res); err != nil {
 		t.Fatalf("decode: %v", err)
 	}
-	if res.Status != address.StatusFound || res.Address != "Станционная улица 1/1" {
+	if res.Status != address.StatusFound || res.Address != "2-я Станционная улица 1/1" {
 		t.Fatalf("unexpected result: %+v", res)
 	}
 }