Enforce fixed 120Hz cadence contract

[yvette-carlisle]

Summary

• update the performance spec to make 120Hz / 8.33ms the hard active-interaction target
• remove refresh-rate-derived scheduling from the Rust overlay and Swift native host paths
• add native-host live chrome telemetry for first visible apply, fast-position cadence, and frame tick gaps
• prewarm HUD/loupe windows and pixel-align live chrome presentation to reduce startup and Retina stepping artifacts

Validation

• cargo make fmt-check
• cargo make lint-swift
• cargo make test-macos-native-host
• cargo make lint-rust
• cargo make test-rust
• git diff --check
• signed release launched from target/rsnap-native-host/rsnap.app for local live-mode telemetry

Notes

• The follow-up direction for moving live HUD/loupe into the overlay CALayer presentation path is intentionally not included here. This PR keeps the current NSWindow-based surface and adds the telemetry needed to evaluate that migration.