feat: add CodeBuddy Code support

[studyzy]

Closes #1966

Summary

Adds first-class support for CodeBuddy Code, a Claude-powered AI coding assistant whose config lives in .codebuddy/.

CodeBuddy Code uses the same PreToolUse hook JSON protocol as Claude Code, so the hook implementation delegates directly to the existing process_claude_payload logic.

Changes

New commands

• rtk hook codebuddy — PreToolUse hook processor (reads JSON from stdin, rewrites tool_input.command)
• rtk init -g --agent codebuddy — installs hook into ~/.codebuddy/settings.json and writes ~/.codebuddy/CODEBUDDY.md
• rtk init -g --agent codebuddy --uninstall — removes all RTK artifacts

Files changed

File	Change
src/hooks/constants.rs	Add CODEBUDDY_DIR (.codebuddy) and CODEBUDDY_HOOK_COMMAND constants
src/hooks/hook_cmd.rs	Add run_codebuddy() — delegates to process_claude_payload
src/hooks/init.rs	Add run_codebuddy_mode(), uninstall_codebuddy(), and patch_settings_json_at() helper
src/main.rs	Add AgentTarget::Codebuddy, HookCommands::Codebuddy, dispatch logic
hooks/codebuddy/rtk-awareness.md	RTK awareness instructions embedded into ~/.codebuddy/CODEBUDDY.md
hooks/codebuddy/README.md	Integration documentation

Design notes

• Zero new protocol code: CodeBuddy Code uses the identical PreToolUse + tool_input.command JSON format as Claude Code, so run_codebuddy() simply calls process_claude_payload().
• patch_settings_json_at(): Extracted a new helper that patches settings.json in an arbitrary directory (instead of hardcoding the Claude config dir). This makes it easy to add future agents with similar config layouts.
• Global-only: Like Gemini and Cursor, CodeBuddy hooks are installed globally (~/.codebuddy/).

Testing

# Hook rewrite works correctly
echo '{"tool_name":"Bash","tool_input":{"command":"git status"}}' | rtk hook codebuddy
# Output: {"hookSpecificOutput":{"hookEventName":"PreToolUse","updatedInput":{"command":"rtk git status"}}}

# Dry-run init
rtk init -g --agent codebuddy --dry-run -v

# All 1901 existing tests pass
cargo test

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