Add Amp CLI support and checkpoint plugin integration

[svarlamov]

Summary

• add Amp agent preset and transcript parsing support
• add Amp plugin installer + plugin template with pre/post checkpoint capture
• wire Amp into install flow and show experimental plugin usage note
• add Amp fixtures and integration coverage

Validation

• cargo fmt -- --check
• cargo clippy
• cargo test --test amp
• cargo test --test install_hooks_comprehensive test_run_install_hooks_no_args -- --exact
• cargo test --test install_hooks_comprehensive test_run_install_hooks_with_dry_run_false -- --exact

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✅ Devin Review: No Issues Found

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

View in Devin Review to see 6 additional findings.