Fix metakey mapped to Control modifier instead of Meta/Super

[Copilot]

The metakey (Super/Windows key) was incorrectly mapped to modifier value 4, causing it to behave as Control. Should be 64 (Mod4 mask).

Changes

• Updated map_mod_key() in virtual_keyboard.rs to return 64 for KEY_LEFTMETA and KEY_RIGHTMETA

fn map_mod_key(key: evdev::KeyCode) -> u32 {
    match key {
        evdev::KeyCode::KEY_LEFTCTRL | evdev::KeyCode::KEY_RIGHTCTRL => 4,
-       evdev::KeyCode::KEY_LEFTMETA | evdev::KeyCode::KEY_RIGHTMETA => 4,
+       evdev::KeyCode::KEY_LEFTMETA | evdev::KeyCode::KEY_RIGHTMETA => 64,
        evdev::KeyCode::KEY_LEFTSHIFT | evdev::KeyCode::KEY_RIGHTSHIFT => 1,
        evdev::KeyCode::KEY_LEFTALT | evdev::KeyCode::KEY_RIGHTALT => 8,
        _ => 0,
    }
}

Standard X11/Wayland modifier masks: Shift=1, Control=4, Alt=8, Meta/Super=64.

No Cargo.lock changes, so cargoHash in flake.nix remains unchanged.

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