feat(config): support configuring preserved messages in compaction

[narcilee7]

Related Issue

N/A (Resolves internal TODO in src/kimi_cli/soul/kimisoul.py)

Description

This PR adds a new configuration option max_preserved_messages to the loop_control section in config.toml.

• Feature: Users can now control the number of recent messages preserved when auto-compaction is triggered.
• Default: The default value is set to 2, maintaining the existing behavior while offering flexibility for users who wish to retain more context.
• Implementation: Updated LoopControl config model and KimiSoul initialization to pass the configured value to SimpleCompaction.

Checklist

• I have read the https://github.com/MoonshotAI/kimi-cli/blob/main/CONTRIBUTING.md document.
• I have linked the related issue, if any.
• I have added tests that prove my fix is effective or that my feature works.
• I have run make gen-changelog to update the changelog.
• I have run make gen-docs to update the user documentation.

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 3 additional findings.