fix: sync IME preedit state with libghostty

[hiddeco]

On US-English keyboards, pressing a dead-key sequence such as Option+E followed by a vowel would leak the intermediate keystroke — e.g. typing " could produce '" because the initial ' compose key was sent as real input. CJK input methods (Korean, Japanese) had similar issues where compose keystrokes were not suppressed.

Port the preedit synchronisation pattern from Ghostty's own SurfaceView_AppKit: track marked-text state before and after interpretKeyEvents, call ghostty_surface_preedit to push the compose string (or clear it), and set the composing flag on key events so libghostty suppresses encoding while a dead-key or IME sequence is active.

Fixes #454

[davidpoblador]

Was the omission of syncPreedit from setMarkedText/unmarkText intentional? Upstream Ghostty calls it from both when not inside a keyDown (keyTextAccumulator == nil) — see SurfaceView_AppKit.swift#L1844-L1857 (v1.3.1, the tag this repo's submodule is pinned to). The upstream comment specifically flags the "change keyboard layout mid-compose" case (set US Intl, type ', switch layout). Curious whether you scoped this down deliberately or just hadn't gotten to it.

[hiddeco]

@davidpoblador oversight, has been added now.

[davidpoblador]

Left-side keys fall through to sidePressed = true, which misreports a release as a press when both sides of a modifier are held. Repro: hold L-Shift, then hold R-Shift, then release L-Shift — the L-Shift release event arrives with keyCode 0x38 and the generic .shift bit still set (R-Shift is held), so sidePressed defaults to true and we send PRESS instead of RELEASE.

Fix is symmetric: check NX_DEVICEL*KEYMASK for left-side keyCodes the same way the right side already does. CapsLock has no L/R pair so the existing default works for it.

Suggested change

	switch event.keyCode {
	case 0x3C:
	sidePressed = event.modifierFlags.rawValue
	& UInt(NX_DEVICERSHIFTKEYMASK) != 0
	case 0x3E:
	sidePressed = event.modifierFlags.rawValue
	& UInt(NX_DEVICERCTLKEYMASK) != 0
	case 0x3D:
	sidePressed = event.modifierFlags.rawValue
	& UInt(NX_DEVICERALTKEYMASK) != 0
	case 0x36:
	sidePressed = event.modifierFlags.rawValue
	& UInt(NX_DEVICERCMDKEYMASK) != 0
	default:
	sidePressed = true
	}
	switch event.keyCode {
	case 0x38:
	sidePressed = event.modifierFlags.rawValue
	& UInt(NX_DEVICELSHIFTKEYMASK) != 0
	case 0x3C:
	sidePressed = event.modifierFlags.rawValue
	& UInt(NX_DEVICERSHIFTKEYMASK) != 0
	case 0x3B:
	sidePressed = event.modifierFlags.rawValue
	& UInt(NX_DEVICELCTLKEYMASK) != 0
	case 0x3E:
	sidePressed = event.modifierFlags.rawValue
	& UInt(NX_DEVICERCTLKEYMASK) != 0
	case 0x3A:
	sidePressed = event.modifierFlags.rawValue
	& UInt(NX_DEVICELALTKEYMASK) != 0
	case 0x3D:
	sidePressed = event.modifierFlags.rawValue
	& UInt(NX_DEVICERALTKEYMASK) != 0
	case 0x37:
	sidePressed = event.modifierFlags.rawValue
	& UInt(NX_DEVICELCMDKEYMASK) != 0
	case 0x36:
	sidePressed = event.modifierFlags.rawValue
	& UInt(NX_DEVICERCMDKEYMASK) != 0
	default:
	sidePressed = true
	}

With this applied, the comment block above (lines 366–369) might want to be tweaked to drop the "for right-side keys" qualifier since both sides are now checked symmetrically.