Disable scroll capture and harden native host validation

[yvette-carlisle]

Summary

• Disable the broken scroll capture entry path while preserving non-scroll capture behavior.
• Move hotkey binding state into a focused coordinator without changing the native-host hotkey semantics.
• Harden HUD-follow smoke gates and update smoke/perf docs to match current script behavior.

Validation

• cargo make fmt-check
• cargo make lint-swift
• cargo make test-macos-native-host
• python3 -m py_compile scripts/smoke/lib/native-hud-follow-summary.py
• bash -n scripts/perf/self-check-macos.sh scripts/perf/macos.sh scripts/smoke/macos.sh scripts/smoke/native-hud-follow-macos.sh
• git diff --check