fix(auth): make JWT authentication optional with fallback

Modify authentication system to gracefully handle cases where JWT is not enabled or token is missing. This includes:
- Making HTTPBearer auto_error=False to prevent automatic 403 errors
- Updating token dependency to return None when JWT is disabled
- Fixing model deserialization in CrawlResult
- Updating documentation links
- Cleaning up imports

BREAKING CHANGE: Authentication behavior changed to be more permissive when JWT is disabled

crawl4ai/async_database.py

@@ -4,10 +4,10 @@ import aiosqlite
 import asyncio
 from typing import Optional, Dict
 from contextlib import asynccontextmanager
-import logging
 import json  # Added for serialization/deserialization
 from .utils import ensure_content_dirs, generate_content_hash
 from .models import CrawlResult, MarkdownGenerationResult, StringCompatibleMarkdown
+# , StringCompatibleMarkdown
 import aiofiles
 from .utils import VersionManager
 from .async_logger import AsyncLogger