revert: premature squash merge of #306 to restore stacked PR workflow

[Aryansharma28]

Reverts the squash merge of #306 from main.

Reason: I (Claude) squash-merged #306 without realizing it would auto-close #340 (whose base was #306's branch). This broke the stacked-PR workflow that was set up. Reverting so #306, #340, #341 can be merged in the proper order.

Auto-generated revert. Will be closed once the proper stacked merge completes.

[github-actions]

Automated low-risk assessment

This PR was evaluated against the repository's Low-Risk Pull Requests procedure and does not qualify as low risk.

The diff makes substantive functional changes (removing the GoatStrategy and GOAT metaprompt, changing CrescendoStrategy/API signatures, moving phase-boundary computation into template rendering, and updating runtime code and tests). These are code- and behavior-level changes to core red-team logic and public/internal APIs, not limited to docs, styling, or trivially revertable test tweaks, so they require normal code review.

This PR requires a manual review before merging.