Fix incorrect chat title generation for reasoning/thinking mode conversations.

[Ayushraj6202]

Root Cause

The title generation logic was including reasoning/thinking content, which caused noisy or irrelevant titles.

Changes
Filtered reasoning content before title generation
Preserved existing behavior for standard chats
Testing
Verified normal chats still generate correct titles
Verified reasoning mode chats now generate accurate titles
Tested with long prompts and multi-turn conversations

Fixes #12338

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Summary by cubic

Fixes noisy chat titles in reasoning/thinking mode by disabling reasoning in the title-generation request so titles only reflect user-visible content. Standard chats are unchanged.

^{Written for commit db1dca0. Summary will update on new commits.}

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[cubic-dev-ai]

No issues found across 1 file