Add Google Gemini as AI provider

- Add gemini.py provider using google-genai SDK
- Update config.py with gemini provider and GEMINI_API_KEY
- Update ai_service.py factory to support gemini
- Add google-genai to requirements.txt
- Update .env.example, README.md, and CLAUDE.md documentation

src/daemon_boyfriend/config.py

@@ -19,7 +19,7 @@ class Settings(BaseSettings):
     discord_token: str = Field(..., description="Discord bot token")
 
     # AI Provider Configuration
-    ai_provider: Literal["openai", "openrouter", "anthropic"] = Field(
+    ai_provider: Literal["openai", "openrouter", "anthropic", "gemini"] = Field(
         "openai", description="Which AI provider to use"
     )
     ai_model: str = Field("gpt-4o", description="AI model to use")
@@ -30,6 +30,7 @@ class Settings(BaseSettings):
     openai_api_key: str | None = Field(None, description="OpenAI API key")
     openrouter_api_key: str | None = Field(None, description="OpenRouter API key")
     anthropic_api_key: str | None = Field(None, description="Anthropic API key")
+    gemini_api_key: str | None = Field(None, description="Google Gemini API key")
 
     # Logging
     log_level: str = Field("INFO", description="Logging level")
@@ -66,6 +67,7 @@ class Settings(BaseSettings):
             "openai": self.openai_api_key,
             "openrouter": self.openrouter_api_key,
             "anthropic": self.anthropic_api_key,
+            "gemini": self.gemini_api_key,
         }
         key = key_map.get(self.ai_provider)
         if not key: