feat(hooks): add inject_prompt for simplified context injection

[Dqz00116]

Related Issue

N/A - This is a new feature proposal for simplifying context injection in hooks.

Description

This PR adds a simplified way to inject context into conversations via the UserPromptSubmit hook.

Changes

1. Added inject_prompt field to HookDef (src/kimi_cli/hooks/config.py)

   • Alternative to command for simple static content injection
   • Supports both inline text and file paths (auto-detected)
   • command and inject_prompt are mutually exclusive

2. Added additional_context support (src/kimi_cli/hooks/runner.py, src/kimi_cli/hooks/engine.py)

   • New field in HookResult to carry context from hooks
   • Parsed from hookSpecificOutput.additionalContext in JSON responses
   • Native support for inject_prompt without spawning subprocess

3. Context injection in KimiSoul (src/kimi_cli/soul/kimisoul.py)

   • Collects additional_context from all hook results
   • Injects as system reminder message before user input processing

4. Documentation (docs/en/customization/hooks.md)

   • Documented inject_prompt field and usage examples
   • Documented additionalContext JSON output

5. Tests (tests/hooks/)

   • Added tests for inject_prompt validation
   • Added tests for additional_context parsing
   • Added integration tests for file-based injection

Usage Example

Static content:

[[hooks]]
event = "UserPromptSubmit"
inject_prompt = "Always write tests first."

From file:
[[hooks]]
event = "UserPromptSubmit"
inject_prompt = "~/.kimi/prompts/coding-guidelines.md"

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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