Windows: add edge-notch auto-hide

[stanthewizzard]

Summary

• add an auto-hide option for the Windows edge notch
• retract the notch to an 8 px tab after the pointer leaves and reveal it on hover
• support left, right, top, and bottom edges
• hide the move/settings handles and decorative fillets while retracted, preventing the visual artifacts outside the tab
• expose Auto-hide / Always visible in Windows settings

Scope

Windows implementation only (windows/codenotch). macOS is unchanged.

Validation

cargo test --release --locked -p codenotch: 100 passed, 0 failed, 2 ignored.

[vinzdg]

Closing — #288 has landed and covers edge auto-hide.

Two things here would have needed fixing first, recording them in case they're useful elsewhere:

• ui/notch.html:27,917 — retracting animates #pill with a 160 ms transform transition, then setRetracted measures via requestAnimationFrame(reportHot) one frame in. getBoundingClientRect reflects the in-progress transform, so the hot rect reported for a retracted notch is close to the full pill: click-through stays off over a large invisible region and the 8 px tab is never the real reveal target. Fold the Windows notch to a pill when not in use, as the Mac's Show on hover does #288 sidesteps this by measuring the static #rest element.
• src/config.rs:133 — default_auto_hide() = true means every existing config starts auto-hiding on update, which the test asserts as intended. Fold the Windows notch to a pill when not in use, as the Mac's Show on hover does #288 reads the raw JSON to tell a fresh install from an upgrade so existing notches stay open.

Also nothing suppressed retraction during begin_move, drag_begin or while the context menu was up, so the pill vanished mid-carry, and the new strings went in via bare .textContent = rather than ui(...), so they'd have been English in every locale.

Thanks @stanthewizzard — and #282 (Z.AI) is still open and worth finishing; I've left review notes on it.