Fix PSP memory stick availability check on real hardware

sceIoGetstat on a bare device root ("ms0:/") returns EINVAL on real
PSP hardware even when a memory stick is present - confirmed via a
diagnostic print during hardware testing. Switched to sceIoDopen/
sceIoDclose, the SDK's own documented way to probe a device root,
which real hardware handles correctly.

Also adds a temporary unconditional settings write once a save device
is selected, to confirm the write path itself works on hardware now
that availability detection is fixed.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/dusklinux/input/inputlinux.c

@@ -517,7 +517,6 @@ errorret_t inputInitLinux(void) {
     X("tab", INPUT_ACTION_CANCEL);
     X("q", INPUT_ACTION_CANCEL);
     X("escape", INPUT_ACTION_RAGEQUIT);
-    X("enter", INPUT_ACTION_PAUSE);
     X("`", INPUT_ACTION_CONSOLE);
   #endif