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.

config.example.json

@@ -17,6 +17,10 @@
     "url": "${ADDRKIT_LLM_URL}",
     "token": "${ADDRKIT_LLM_TOKEN}",
     "model": "qwen3-14b-awq",
-    "timeout_seconds": 3
+    "timeout_seconds": 3,
+    "max_tokens": 512,
+    "disable_thinking": true,
+    "system_prompt": "",
+    "system_prompt_file": ""
   }
 }