adk: bridge last_call for LiteLlm/Gemini built from connection_kwargs() #1218

Current behavior (verified)

#1214 fixed donkey.adk.model() / gemini() on google-adk ≥ 2.13: they return _last_call_bridged_class(...) subclasses (python/src/donkey_kit/integrations/adk.py:217). A model built by hand is not bridged:

• LiteLlm(model=..., **donkey.adk.connection_kwargs()) (website/content/frameworks/adk.mdx:98)
• Gemini(..., **donkey.adk.gemini_connection_kwargs()) (website/content/frameworks/adk.mdx:151)

On 2.13+ its after_model_callback reads UNOBSERVED; on 2.12 it read OBSERVED. adk.mdx:264-265 documents the gap, but no test pins it and no issue tracked it until now.

Proposal

• Expose a public way to bridge user-built models: either a public governed class, or a helper that wraps an existing BaseLlm.
• Add a Runner + after_model_callback test for the hand-built path.
• Update adk.mdx and the docs/verified-apis.md §8 ADK rows.

Cross-surface impact

• integrations/: in scope (integrations/adk.py).
• Nextra docs site: in scope (frameworks/adk.mdx).
• docs/verified-apis.md: §8 ADK rows get a dated offline re-check entry.
• core/: not affected (reuses open_last_call_bridge).
• llm/, registry/, tools/, CLI: not affected.
• TypeScript parity: not affected; no TS code exists yet.

Refs #1207, #1214.