feat: add Cline/Roo Code support via rtk init --agent cline

Summary

Add Cline (VS Code) support to RTK.

How Cline works

Cline uses .clinerules file in project root for custom rules, and hooks in ~/Documents/Cline/Rules/Hooks/ or .clinerules/hooks/ for scripts.

PreToolUse hooks can cancel commands but cannot rewrite them. contextModification injects text into conversation context.

Implementation

Rules-based approach (like Windsurf/Codex):

• rtk init --agent cline creates .clinerules with RTK instructions
• Optional: PreToolUse hook for tracking via rtk gain

References

• Cline Hooks docs
• Cline Rules docs