Add Copilot support and fix Windows startup

[timeshift92]

Add explicit GitHub Copilot integration for both repository-local and global setup, wire the Copilot hook asset to
tk hook copilot, document the new workflow, and add focused tests for the new assets and CLI parsing.

Also fix the Windows startup stack overflow by reserving a larger main-thread stack at link time so
tk.exe --version, --help, and Copilot hook entry points start reliably on Windows.

Summary

Test plan

• cargo fmt --all && cargo clippy --all-targets && cargo test
• Manual testing: rtk <command> output inspected

Important: All PRs must target the develop branch (not master).
See CONTRIBUTING.md for details.

[CLAassistant]

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[pszymkowiak]

[w] wshm · Automated triage by AI

📊 Automated PR Analysis

✨ Type	feature
🟡 Risk	medium

Summary

Adds explicit GitHub Copilot integration with both global and repository-local setup modes, updates the hook command from 'rtk hook' to 'rtk hook copilot', and fixes a Windows startup stack overflow by reserving an 8 MiB main-thread stack at link time in build.rs.

Review Checklist

• Tests present
• Breaking change
• Docs updated

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Analyzed automatically by wshm · This is an automated analysis, not a human review.