Add image content block handling to ClaudeProviderHandler:

1. Image Extraction (_extract_images_from_content):
   - Extract images from OpenAI message content format
   - Handle base64 data URLs (data:image/jpeg;base64,...)
   - Handle HTTP/HTTPS URL-based images
   - Convert to Anthropic image source format
   - Validate image size (5MB limit for base64)
   - Pass through existing Anthropic-format image blocks

2. Image Integration in Message Conversion:
   - Extract images from user message content blocks
   - Convert image_url blocks to Anthropic image source format
   - Add image blocks to anthropic_messages content array
   - Preserve text content alongside images

Reference: vendors/kilocode image handling + vendors/claude multimodal support