keyboard, hyprland/ipc: keyboard layout handling

[brainrom]

Adds keyboard layout support to the Hyprland backend, inspired by the equivalent Waybar module.

Problem

QuickShell had no way to query or switch keyboard layouts under Hyprland or any other environment. Users who wanted a layout indicator or switcher had to resort to external tools.

Solution

Two new components:

Quickshell.Keyboard (src/keyboard/) — A compositor-agnostic KeyboardLayout data class that resolves xkb layout names via libxkbregistry. Can be reused by future compositor backends (Sway, etc.) since the layout model is the same regardless of the compositor.

HyprlandKeyboard (Quickshell.Hyprland._Ipc) — Hyprland-specific keyboard device representation. Maintains an ObjectModel<KeyboardLayout> of available layouts, tracks the active one, and exposes cycleLayout() / switchToLayout(index) for switching.

Commits

The change is split into three commits, each independently reviewable:

Commit	Scope
keyboard: new module for keyboard layouts (data class)	New Quickshell.Keyboard module with the shared KeyboardLayout class and xkbregistry resolution logic.
hyprland/ipc: make dispatch prefix in dispatch() optional	Enables sending raw Hyprland commands (like switchxkblayout) without the dispatch prefix, mirroring hyprctl behavior, since switchxkblayout isn't available through Hyprland's Lua/legacy dispatcher.
hyprland/ipc: keyboard layout handling	HyprlandKeyboard device tracking, j/devices parsing, activelayout event handling, and layout switching via switchxkblayout.

QML API additions

import Quickshell.Hyprland

Hyprland.keyboards              // model of HyprlandKeyboard
Hyprland.activeKeyboard         // last device that sent activelayout
Hyprland.activeKeyboardChanged  // signal

// HyprlandKeyboard
keyboard.name                   // device name
keyboard.activeLayout           // KeyboardLayout*
keyboard.activeLayoutIndex      // int
keyboard.availableLayouts       // model of KeyboardLayout
keyboard.cycleLayout()
keyboard.switchToLayout(index)

// KeyboardLayout (Quickshell.Keyboard)
layout.shortName                // "us" | "de" | "fr" | "ru" | "ua"
layout.variant                  // "intl", ""
layout.shortDescription         // "English" | "German" | "French" | "Russian" | "Ukrainian"
layout.fullName                 // "English (US, intl., with dead keys)", etc.

Checklist

• clang-format passes on all new/modified files
• Builds with default options
• module.md for new module added, new files added to corresponding module.md, docs tested