docs(sdk): add conversation model switching example

[enyst]

• I have read and reviewed the documentation changes to the best of my ability.
• If the change is significant, I have run the documentation site locally and confirmed it renders as expected.

Summary of changes

• document examples/01_standalone_sdk/44_model_switching_in_convo.py under the existing LLM Profile Store guide
• add an auto-synced expandable code block and run snippet for the mid-conversation switch_profile() flow
• keep this PR scoped to the missing example 44 docs; the lifecycle example docs remain tracked separately in docs(sdk): sync plugin and skill lifecycle examples #386

Related SDK example: OpenHands/software-agent-sdk/blob/main/examples/01_standalone_sdk/44_model_switching_in_convo.py

[all-hands-bot]

🟢 Good taste - Accurate, well-structured documentation.

Verified against agent-sdk source: example file exists, code matches exactly, all imports and methods are correct. Follows established patterns. This is solid work.