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/test_utils.py

@@ -0,0 +1,48 @@
+"""Tests for utility functions."""
+
+from datetime import timedelta
+
+import pytest
+
+from guardden.cogs.moderation import parse_duration
+
+
+class TestParseDuration:
+    """Tests for the parse_duration function."""
+
+    def test_parse_seconds(self) -> None:
+        """Test parsing seconds."""
+        assert parse_duration("30s") == timedelta(seconds=30)
+        assert parse_duration("1s") == timedelta(seconds=1)
+
+    def test_parse_minutes(self) -> None:
+        """Test parsing minutes."""
+        assert parse_duration("5m") == timedelta(minutes=5)
+        assert parse_duration("30m") == timedelta(minutes=30)
+
+    def test_parse_hours(self) -> None:
+        """Test parsing hours."""
+        assert parse_duration("1h") == timedelta(hours=1)
+        assert parse_duration("24h") == timedelta(hours=24)
+
+    def test_parse_days(self) -> None:
+        """Test parsing days."""
+        assert parse_duration("7d") == timedelta(days=7)
+        assert parse_duration("1d") == timedelta(days=1)
+
+    def test_parse_weeks(self) -> None:
+        """Test parsing weeks."""
+        assert parse_duration("2w") == timedelta(weeks=2)
+        assert parse_duration("1w") == timedelta(weeks=1)
+
+    def test_invalid_format(self) -> None:
+        """Test invalid duration formats."""
+        assert parse_duration("invalid") is None
+        assert parse_duration("") is None
+        assert parse_duration("10") is None
+        assert parse_duration("abc") is None
+
+    def test_case_insensitive(self) -> None:
+        """Test that parsing is case insensitive."""
+        assert parse_duration("1H") == timedelta(hours=1)
+        assert parse_duration("30M") == timedelta(minutes=30)