fix: polish Wayland gaming shortcuts UI

[Retr0astic]

Summary

This PR adds a configurable Linux DualSense gaming-shortcuts layer to the companion application, built on the existing controller input, settings, IPC, and notification infrastructure.

Gaming shortcuts

• Adds PS-button gesture recognition for single press, double press, long press, and PS-plus-button chords.
• Adds an optional temporary shortcut mode with a timeout, shortcut reference notification, and PS/Circle cancellation.
• Stores global bindings and per-game overrides, with runtime override selection using the active-game watcher from Trigger Profiles.
• Supports configurable actions for:
  • opening/focusing OpenDS5
  • launching an application or custom executable
  • volume up/down/mute and microphone mute toggle
  • screenshots
  • screen recording
  • performance HUD toggle
  • on-screen keyboard
  • passthrough and no-op behavior
• Adds timing controls for double-press, long-press, and chord recognition.
• Adds success/error notification preferences, action-result notifications, and a notification preview.
• Adds best-effort Linux environment/provider detection and structured unavailable/failed action results.
• Validates persisted action types, rejects NUL-containing executable/argument values, and limits executable argument arrays to 64 entries. Actions use argument arrays rather than shell execution.

Controller and runtime integration

• Adds Linux evdev discovery for the physical DualSense gamepad node while excluding touchpad, sensor, headset, and other sibling nodes.
• Associates evdev sources with matching HID paths for shortcut-result metadata and lifecycle tracking.
• Adds DualSense button handling for the PS button, touchpad, mute, L3/R3, and D-pad events.
• Normalizes hat/D-pad input into controller button events and preserves controller source identity through the input pipeline.
• Wires the reader, gesture coordinator, action executor, settings store, IPC, preload API, notifications, and application lifecycle together.
• Cleans up readers, gesture timers, shortcut-mode notifications, and source state during disconnect, reload, and application shutdown.
• Broadens Linux audio-sink matching with a four-channel “Wireless Controller” fallback heuristic.

Companion UI and settings

• Adds a Gaming Shortcuts control tab with:
  • enable/disable toggle
  • PS gesture editors
  • direct-chord editor
  • shortcut-mode settings
  • timing and notification controls
  • per-game override editor
  • reset and preset actions
  • controller preview and provider availability status
• Persists and normalizes gaming-shortcut settings, including malformed persisted actions and bounded executable arguments.
• Restores stick sample preview forwarding and improves the preview layout for narrow windows.
• Forces a repaint after native resize on Linux/Wayland to avoid stale transparent regions in frameless windows.
• Replaces the static controller preview messaging with the new interactive gaming-shortcuts preview.

Development and Nix support

• Adds tracked Codex planner, implementer, reviewer, and repository-agent configuration.
• Extends the Nix development shell with the toolchain and Linux utilities needed for companion development and shortcut providers.
• Adds the OpenDS5 Cachix substituter and trusted key for Nix development/build caching.

Validation

• GitHub nix-flake check: passed.
• GitHub release AppImage check: passed.
• git diff --check upstream/dev...HEAD: passed.
• cd ds5-bridge/companion && npm run typecheck: passed.
• cd ds5-bridge/companion && ./node_modules/.bin/vitest run src: passed (57 files, 773 tests).
• Changed shortcut/evdev/settings/UI tests: passed (15 files, 197 tests).
• cd ds5-bridge/companion && npm run test:installer: passed (16 checks).

The full native, firmware, and Nix rebuild pipelines were not freshly run locally. Hardware/manual controller validation was not performed.

Known limitations

• Runtime shortcut input is Linux-only; the settings UI can still be rendered and saved on other platforms.
• Desktop actions are global. Input-source/HID association is currently used for metadata and lifecycle tracking; it does not suppress an unmatched controller or provide per-controller action isolation.
• Provider detection is best-effort and depends on external tools such as wpctl, wtype, grim, hyprshot, gpu-screen-recorder, and MangoHud configuration. The four-channel wireless-controller sink fallback may require additional validation when multiple controllers are connected.
• Queued actions and child processes are not currently cancelled when a controller disconnects or the application shuts down.
• Per-game override selection depends on Trigger Profiles active-game detection.
• Steam Input compatibility, native DualSense game compatibility, wired/Bluetooth combinations, multiple-controller routing, desktop-provider behavior, and physical DualSense input remain unverified.