keymon: Refresh system state before acting on SELECT

[robcodedev]

Fix intermittent SELECT -> MENU shortcut on Miyoo Mini v4 and Miyoo Flip.

system_state is a cached value, only re-read when /tmp/state_changed
exists, on a MENU press, or from deepsleep(). Two situations can leave it
wrong:

• after a fresh boot it's still MODE_UNKNOWN
• after returning from a game it's sometimes stale, when keymon consumes
  /tmp/state_changed before MainUI is back up

In both cases the SELECT -> MENU shortcut compares against the wrong value and
does nothing. It starts working once a state transition or MENU press forces an
update, which made it look intermittent rather than broken.

This re-reads the state in the handler before branching on it. The call sits
behind !comboKey_select && val == RELEASED, so it runs once per SELECT tap.

Scope

Deliberately limited to SELECT. Five other handlers read the same cached value
and might have the same problem, but I couldn't reproduce any issues with
other key presses.

Open question

Reported on v4 and Flip but not on Plus. I couldn't find a device-dependent
path in the state logic to explain that, so if anyone knows where the boot
ordering differs I'd like to hear it. The fix isn't device-specific either way.

Testing

• Fresh boot, SELECT as the first input: shortcut works
• Launch a game, exit back to MainUI, SELECT: shortcut works
• SELECT combos still behave as before