Phase 17: Multimodal image understanding via analyze_image tool

Dual-model approach (C): Qwen3-8B handles conversation, Qwen2.5-VL-7B
analyzes images on demand via analyze_image LangChain tool.

- services/model/mlx_vision_model.py: MlxVisionModel (mlx-vlm wrapper, lazy load)
- services/agent/tools.py: make_vision_tool(vision_model, image_path)
- agent_service.py: stream_response(image_path=None), dynamic tool binding
  via config["image_path"] — thread-safe per-request rebinding
- container.py: vision_model Singleton provider
- config.py: vision_enabled, vision_model_id, vision_max_tokens
- api.py: image_base64 in ChatRequest, decode to temp file, cleanup after stream

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

services/model/mlx_vision_model.py

@@ -0,0 +1,48 @@
+"""Qwen2.5-VL (mlx-vlm) 기반 이미지 분석 서비스.
+
+첫 analyze() 호출 시 모델을 lazy load해 메모리를 아낀다.
+"""
+from __future__ import annotations
+
+import logging
+
+logger = logging.getLogger(__name__)
+
+_DEFAULT_PROMPT = "이 이미지를 한국어로 자세히 설명해줘. 사람, 음식, 문서 등 보이는 것을 빠짐없이 설명해."
+
+
+class MlxVisionModel:
+    def __init__(self, model_id: str, max_tokens: int = 512) -> None:
+        self._model_id = model_id
+        self._max_tokens = max_tokens
+        self._model = None
+        self._processor = None
+
+    def _load(self) -> None:
+        if self._model is not None:
+            return
+        logger.info("Vision 모델 로딩 중: %s", self._model_id)
+        from mlx_vlm import load
+        self._model, self._processor = load(self._model_id)
+        logger.info("Vision 모델 로딩 완료")
+
+    def analyze(self, image_path: str, prompt: str = _DEFAULT_PROMPT) -> str:
+        """이미지를 분석해 한국어 설명을 반환한다."""
+        self._load()
+        from mlx_vlm import generate
+        from mlx_vlm.prompt_utils import apply_chat_template
+        from mlx_vlm.utils import load_config
+
+        config = load_config(self._model_id)
+        formatted_prompt = apply_chat_template(
+            self._processor, config, prompt, num_images=1
+        )
+        result = generate(
+            self._model,
+            self._processor,
+            image=image_path,
+            prompt=formatted_prompt,
+            max_tokens=self._max_tokens,
+            verbose=False,
+        )
+        return result if isinstance(result, str) else str(result)