feat(control): add verified clamshell mutations

[LMLiam]

Goal

Add idempotent enable, disable, and toggle operations through a helper that accepts no arbitrary privileged command.

Acceptance criteria

• Skip unnecessary mutations.
• Map enabled and disabled to the exact battery-only pmset commands.
• Require effective UID zero and accept only one literal helper argument.
• Invoke the helper through sudo -n.
• Verify final state before success.
• Support quiet output without hiding errors.

Owned files

ClamshellService.swift, PrivilegedHelperClient.swift, ClamshellHelper.swift, mutation commands, and their tests.

Dependencies

Read-only state support.

Verification

swift test --filter ClamshellServiceTests
swift test --filter PowerMutationTests
swift test --filter PrivilegedHelperClientTests
swift test
swift build -c release

Plan: Phase 3, Tasks 5–7