feat(remap): add cascading action selector

[blak0p]

Closes #78

Summary

• Replaces the flat remap action popup with Basic/Multimedia cascading menus.
• Keeps the menu visible inside scrollable panels and constrains it to the viewport.
• Preserves Button 1 restrictions, staging behavior, and Apply/Discard shortcuts.

Changes

File	Change
frontend/src/components/panels/GnomeSelect.tsx	Adds accessible category/submenu navigation, portal placement, and viewport-aware positioning.
frontend/src/components/panels/GnomeSelect.test.tsx	Covers pointer, keyboard, portal, scroll, and disabled-action behavior.
frontend/src/styles/controls.css	Adds responsive menu/submenu sizing and visibility behavior.
odd/tasks/cascading-remap-selector.md	Records strict-TDD evidence and manual verification.

Hardware impact

No device write, hidraw operation, or Apply action was performed. This is a frontend-only presentation change.

Test Plan

• Focused selector/panel tests — 10 tests
• Full frontend suite — 86 tests
• go test ./... — 313 tests
• go vet ./...
• go build ./... && (cd frontend && npm run build)
• Manual desktop verification of menu visibility and responsive submenu placement

Delivery note

Native reviewer capture was unavailable for this candidate. The maintainer explicitly elected to deliver without native review.

Depends on #79.