fix: make keymap SVG keys findable with VoiceOver

[mondalaci]

Summary

• Name each keymap key from its physical QWERTY position plus the current mapping (Up Arrow, Up Arrow, unassigned, I, Up Arrow) so VoiceOver can find icon-only and empty keys.
• Keep that name in aria-label, an SVG <title>, and a near-invisible <text> node; VoiceOver often ignores aria-label on SVG <g> and skips keys that have no text.
• Hide the off-screen layer keyboard after a slide, and hide the keyboard while the remap popover is open, so the accessibility tree matches what is on screen.

This is the Agent-side fix for a VoiceOver user who could not locate Mod-layer arrow keys: Home/End have text captions, arrows are icons, and unmapped keys previously had no usable name.

Test plan

• On QWERTY for Mac, Base layer: VoiceOver item chooser search for arrow finds the four physical arrow keys.
• Switch to Mod: search for arrow still finds the letter-row Up key (I, Up Arrow or similar) and the physical up-arrow (Up Arrow, unassigned).
• VO-left/right between Home and End on Mod stops on the Up key in the middle.
• After switching layers, item chooser does not list a duplicate Base-layer keyboard.
• Activate a key: focus moves into the Remap key dialog; Cancel returns to the keyboard; keys behind the overlay are not in the VoiceOver list.
• Sighted remap flow is unchanged (click key, remap, cancel, layer slide).

Made with Cursor