Adapt historical Foundry capabilities onto the UCF transition loop

[sinethxyz]

Objective

Prove that the generalized UCF boundary can carry the concrete machinery that originally lived inside Unicorn Foundry.

Changes

• gives TransitionVerifier access to the execution workspace, an interface requirement exposed by real deterministic verification
• extracts protected-path / migration-guard policy from RunEngine so legacy and UCF paths share one safety rule
• adds GitStateObserver for explicit before/after repository state
• adapts the existing artifact store into a durable TransitionJournal
• adds Foundry planner, executor, verifier, and runtime adapters around the existing AgentRunner / VerificationRunner / WorktreeManager
• preserves deterministic verification, blind review, migration-guard behavior, and REQUEST_CHANGES-as-advisory semantics
• adds an integration test using a real temporary Git repository and real worktree isolation
• updates the runtime-decoupling audit and agent guidance so future migrations use this adapter path

Boundary

This does not replace RunEngine yet and does not make PR publication part of the general transition definition. It establishes the concrete adapter path needed for runtime convergence.

Verification

Current head is green in GitHub Actions:

• editable install: pass
• compileall: pass
• targeted Ruff: pass
• UCF / Foundry adapter tests: 21 passed
• full regression suite: 495 passed