Found docs updates needed from ADK python release v2.9.0 to v2.9.1

[adk-bot]

Compare URL: google/adk-python@v2.9.0...v2.9.1

1. Update Claude adaptive thinking documentation to mention summarized thoughts and version requirements.

Doc file: docs/agents/models/agent-platform.md

Current state:

Newer Claude models support adaptive extended thinking, where the model chooses
its reasoning depth itself rather than using a fixed token budget. On the native
Claude path, a negative thinking_budget maps to adaptive thinking.

Proposed Change:

Newer Claude models support adaptive extended thinking, where the model chooses
its reasoning depth itself rather than using a fixed token budget, and returns its reasoning as summarized thoughts. On the native
Claude path, a negative thinking_budget maps to adaptive thinking. Adaptive thinking is required for Claude Opus 4.7 and later models, and recommended for Opus 4.6 and Sonnet 4.6 where standard "enabled" thinking is deprecated.

Reasoning:
The Python code for Anthropic models now adds display="summarized" to the adaptive thinking config. Additionally, the comments specify that adaptive thinking is now required for Claude Opus 4.7+ and recommended for Opus 4.6/Sonnet 4.6 where the old fixed budget "enabled" mode is deprecated. The documentation should be updated to reflect this behavior and provide this guidance.

Reference: src/google/adk/models/anthropic_llm.py