docs(models): fix unparseable snippets and stale Claude setup steps

[GWeale]

Corrections to the docs/agents/models/ pages: two Python snippets that don't parse, a wrapper class name that doesn't exist, and setup steps that no longer match ADK 2.5.0.

Changes

• docs/agents/models/google-gemini.md — the Python snippet had unbalanced parentheses and would not parse; added the missing , and closing ).
• docs/agents/models/google-gemma.md — the vLLM snippet was missing a comma after extra_headers=auth_headers (syntax error); added it. Also added a note that Gemma 3 needs Gemma (Gemini API) or Gemma3Ollama (Ollama) from google.adk.models, since it has no native function calling or system instruction support.
• docs/agents/models/apigee.md — the wrapper was called ApigeeLLM; the class is ApigeeLlm.
• docs/agents/models/agent-platform.md, docs/agents/models/anthropic.md — removed the LLMRegistry.register(Claude) setup step and its imports: the registry already routes claude-3-* / claude-*-4* strings to Claude. Documented passing Claude(model=...) for identifiers outside those patterns, and corrected the thinking_level note — it raises a validation error on AnthropicGenerateContentConfig and is ignored with a warning on a plain types.GenerateContentConfig.
• docs/agents/models/litellm.md, docs/agents/models/agent-platform.md — pip install litellm → pip install "litellm>=1.84", the version ADK requires.
• docs/agents/models/litert-lm.md — the base_url example omitted the scheme; now http://localhost:8001.

How this was produced

Part of a page-by-page audit of the Python docs against the google/adk-python v2.5.0 source: every import resolved against a real 2.5.0 install, every constructor kwarg checked against model_fields / inspect.signature, every documented default read off the field. A second independent pass re-derived each claim from source rather than trusting the finding, and a third conformed the new wording to the surrounding pages. mkdocs build --strict is clean.

Only Python tabs and language-neutral prose were touched — this audit had no ground truth for the Go / Java / TypeScript SDKs.

Split out of a larger audit branch so each area can be reviewed on its own.

[netlify]

✅ Deploy Preview for adk-docs-preview ready!

Name	Link
🔨 Latest commit	88efcd4
🔍 Latest deploy log	https://app.netlify.com/projects/adk-docs-preview/deploys/6a6a99831680e60009864e71
😎 Deploy Preview	https://deploy-preview-2012--adk-docs-preview.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.
🤖 Make changes	Run an agent on this branch

---

To edit notification comments on pull requests, go to your Netlify project configuration.