feat: Claude Opus via cliproxy 프록시 설정 + base_url 지원

- ClaudeWriter에 base_url 파라미터 추가 (프록시 지원)
- engine.json: provider=claude, cliproxy.gru.farm 프록시 설정
- fallback_chain: claude → gemini → groq 순서

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

bots/engine_loader.py

@@ -66,13 +66,14 @@ BaseVideoGenerator = object
 # ─── Writer 구현체 ──────────────────────────────────────
 
 class ClaudeWriter(BaseWriter):
-    """Anthropic Claude API를 사용하는 글쓰기 엔진"""
+    """Anthropic Claude API를 사용하는 글쓰기 엔진 (프록시 base_url 지원)"""
 
     def __init__(self, cfg: dict):
         self.api_key = os.getenv(cfg.get('api_key_env', 'ANTHROPIC_API_KEY'), '')
-        self.model = cfg.get('model', 'claude-opus-4-5')
+        self.model = cfg.get('model', 'claude-sonnet-4-6')
         self.max_tokens = cfg.get('max_tokens', 4096)
         self.temperature = cfg.get('temperature', 0.7)
+        self.base_url = cfg.get('base_url', '')  # 프록시 URL (옵션)
 
     def write(self, prompt: str, system: str = '') -> str:
         if not self.api_key:
@@ -80,7 +81,10 @@ class ClaudeWriter(BaseWriter):
             return ''
         try:
             import anthropic
-            client = anthropic.Anthropic(api_key=self.api_key)
+            client_kwargs = {'api_key': self.api_key}
+            if self.base_url:
+                client_kwargs['base_url'] = self.base_url
+            client = anthropic.Anthropic(**client_kwargs)
             kwargs: dict = {
                 'model': self.model,
                 'max_tokens': self.max_tokens,