chore: phase 6 replay/compare slice extraction

[Lythaeon]

Summary

• extract replay/compare playback state transitions into an application-layer use-case module
• keep terminal keyboard handling and rendering in adapter loops for replay/compare
• record phase 6 completion artifacts in the hexagonal migration plan

Changes

• add src/application/replay_compare.rs with playback state, actions, tick advancement, range helpers, and unit tests
• refactor src/app/replay/runner.rs and src/app/compare.rs to delegate state transitions to the new use-case module
• alias replay adapter state to the application playback state via src/app/replay/state.rs
• update docs/architecture/ard/ARCHITECTURE_RISKS_HEXAGONAL_PLAN.md with phase 6 artifacts

Checks

• cargo make format
• cargo make clippy
• cargo make test
• cargo make architecture-check