Implement GuardDen Discord moderation bot

Features:
- Core moderation: warn, kick, ban, timeout, strike system
- Automod: banned words filter, scam detection, anti-spam, link filtering
- AI moderation: Claude/OpenAI integration, NSFW detection, phishing analysis
- Verification system: button, captcha, math, emoji challenges
- Rate limiting system with configurable scopes
- Event logging: joins, leaves, message edits/deletes, voice activity
- Per-guild configuration with caching
- Docker deployment support

Bug fixes applied:
- Fixed await on session.delete() in guild_config.py
- Fixed memory leak in AI moderation message tracking (use deque)
- Added error handling to bot shutdown
- Added error handling to timeout command
- Removed unused Literal import
- Added prefix validation
- Added image analysis limit (3 per message)
- Fixed test mock for SQLAlchemy model

src/guardden/services/ai/factory.py

@@ -0,0 +1,67 @@
+"""Factory for creating AI providers."""
+
+import logging
+from typing import Literal
+
+from guardden.services.ai.base import AIProvider
+
+logger = logging.getLogger(__name__)
+
+
+class NullProvider(AIProvider):
+    """Null provider that does nothing (for when AI is disabled)."""
+
+    async def moderate_text(self, content, context=None, sensitivity=50):
+        from guardden.services.ai.base import ModerationResult
+
+        return ModerationResult()
+
+    async def analyze_image(self, image_url, sensitivity=50):
+        from guardden.services.ai.base import ImageAnalysisResult
+
+        return ImageAnalysisResult()
+
+    async def analyze_phishing(self, url, message_content=None):
+        from guardden.services.ai.base import PhishingAnalysisResult
+
+        return PhishingAnalysisResult()
+
+    async def close(self):
+        pass
+
+
+def create_ai_provider(
+    provider: Literal["anthropic", "openai", "none"],
+    api_key: str | None = None,
+) -> AIProvider:
+    """
+    Create an AI provider instance.
+
+    Args:
+        provider: The provider type to create
+        api_key: API key for the provider
+
+    Returns:
+        AIProvider instance
+
+    Raises:
+        ValueError: If provider is unknown or API key is missing
+    """
+    if provider == "none":
+        logger.info("AI moderation disabled")
+        return NullProvider()
+
+    if not api_key:
+        raise ValueError(f"API key required for {provider} provider")
+
+    if provider == "anthropic":
+        from guardden.services.ai.anthropic_provider import AnthropicProvider
+
+        return AnthropicProvider(api_key)
+
+    if provider == "openai":
+        from guardden.services.ai.openai_provider import OpenAIProvider
+
+        return OpenAIProvider(api_key)
+
+    raise ValueError(f"Unknown AI provider: {provider}")