fix(ui): forward thinking configuration to gateway

[Kaguya-19]

Summary

• Forward the Composer thinking configuration through the bridge and Gateway protocol.
• Carry one-turn thinking settings through AgentSession and TurnRunner into AgentLoop.
• Add regression coverage for Gateway propagation and runtime-default override behavior.

Validation

• Root TypeScript check passed.
• 11 focused tests passed.
• UI bridge tests passed: 42 tests.
• UI typecheck remains blocked by the repository\x27s existing React 19 type incompatibilities (TS2786).