Expand Anthropic docs page (extended thinking, vision, tool use)

[AmitoVrito]

Expand docs/llms/anthropic.md from 36 lines to a full provider guide:

• All Claude models with context windows and pricing (claude-opus-4-6, claude-sonnet-4-6, claude-haiku-4-5)
• Extended thinking mode
• Vision with ImageContent
• Tool use / function calling with multiple tools
• Long context strategies
• Cost with CostTracker
• LLMConfig fields, streaming

[AmitoVrito]

Completed in PR #99 — anthropic.md expanded to 236 lines with tool_use, multimodal, extended thinking.