fix(keyboard): apply numlock state on startup and after resume

[H09-0]

Summary

The numlock LED state is not restored after resuming from suspend. While there are GSettings keys to store and remember the numlock state (remember-numlock-state, numlock-state), no code in cinnamon-settings-daemon actually reads or applies them.

Changes

• apply_numlock() – reads remember-numlock-state and numlock-state from GSettings and applies the LED state via XkbLockModifiers. No-ops on Wayland, when remember-numlock-state is false, or when the stored state is unknown.
• logind proxy – connects to org.freedesktop.login1.Manager and listens for PrepareForSleep(false) to re-apply the numlock state after resume.
• Startup path – apply_numlock() is called from apply_all_settings() so the stored state is applied when the keyboard plugin starts.

A minimal, focused fix: no new schema keys, no dynamic state tracking, no key listeners.

[mtwebster]

This was deliberately removed in a2a6017. Muffin handles this. Unfortunately it's only been restoring at resume for Wayland sessions until now:

linuxmint/muffin@6cd3046