refactor(settings): split agents section helpers

[luoye520ww]

Summary

• Splits pure helper logic out of the large Agents settings section into settings-section-agents-utils.
• Covers MCP permission summaries, Skill permission summaries, model context labels, compact list labels, and token economy savings loading from the new helper module.
• Keeps the settings UI and state update paths unchanged.

Why

This is a small frontend performance/maintainability split. settings-section-agents.tsx was carrying pure parsing and summary logic inline, which made the lazy-loaded settings chunk harder to review and evolve. This PR moves that logic behind targeted tests without introducing a new runtime path.

Tests

• npm.cmd test -- src/renderer/src/components/settings-section-agents-utils.test.ts src/renderer/src/components/settings-section-agents.test.ts
• npm.cmd run typecheck
• npm.cmd run build
• git diff --check kunagent/develop...HEAD

Note: the build still reports the existing MessageTimeline static/dynamic import warning on current develop. That warning is addressed separately by #820 and is not introduced by this PR.

[XingYu-Zhong]

Reviewed via Codex triage; approved for merge.