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

tests/conftest.py

@@ -0,0 +1,15 @@
+"""Pytest fixtures for GuardDen tests."""
+
+import pytest
+
+
+@pytest.fixture
+def sample_guild_id() -> int:
+    """Return a sample Discord guild ID."""
+    return 123456789012345678
+
+
+@pytest.fixture
+def sample_user_id() -> int:
+    """Return a sample Discord user ID."""
+    return 987654321098765432