feat(workbench): hide Dock for locked layouts

[devRickyyy]

What changed

• remove the standalone Dock auto-hide prop, timers, handle, and custom activation geometry
• preserve the existing fullscreen immersive Dock behavior and its original CSS hover zone
• treat an active locked layout as the same immersive state as a fullscreen window
• keep the Dock visible for ordinary unlocked workspaces, including an empty workspace
• cover unlocked, fullscreen, locked-layout, and lock-release state transitions

Why

When TSH automatic layout applies a locked Workbench layout, the Dock should behave exactly as it already does for fullscreen windows. A separate user preference and interaction state machine are unnecessary and create inconsistent hover behavior.

Impact

There is no new public prop or persistence contract. Existing fullscreen behavior remains unchanged; consumers with a locked layout now receive the same Dock hiding and edge-hover reveal behavior. The change is platform-neutral React state and CSS behavior, with no operating-system API, path, process, or filesystem impact.

Validation

• pnpm check:changed
• pre-push pnpm check:changed -- --push-ready
• pnpm --filter @tutti-os/workbench-surface typecheck
• pnpm --filter @tutti-os/workbench-surface test (276 core tests and 53 Vitest tests)
• focused WorkbenchDockFrame coverage under jsdom
• downstream TSH preference cleanup: 53 focused tests and pnpm --dir apps/tsh-desktop check

Documentation

No durable documentation change is needed because this extends the existing internal immersive Dock state without adding a public API or configuration surface.