Add R on the main menu to boot Swiss and leave the test app

Getting back to Swiss previously meant power-cycling the console.  R boots
/boot.dol from the SD card directly.

It reuses netboot_boot_file(), so there is ONE DOL launcher and one set of
safety checks (MEM1 entry point, section overlap against the reserved staging
region, libfat unmounted before the jump) rather than a second copy to keep in
step.

Confirmed rather than one-touch, and main-menu only: R is an easy trigger to
catch by accident, test results are not saved anywhere, and losing a full run
to a stray press is worse than one extra button press.  Inside a suite R would
be easy to hit while navigating, so it is ignored there.

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

gc_bba_test/README.md

@@ -73,6 +73,19 @@ Builds clean (no warnings) with devkitPPC 16.1.0 / GCC 16 in the devcontainer:
 
 `.gitignore` excludes the build products — run `make` to produce the `.dol`.
 
+## Boot Swiss (R button)
+
+**R** on the main menu boots `/boot.dol` from the SD card and leaves the test
+app, so you can get back to Swiss without power-cycling the console.
+
+It asks for confirmation (A to go, B to cancel). R is an easy trigger to catch
+by accident, test results are not saved anywhere, and losing a full run to a
+stray press is worse than one extra button. It is also main-menu only — inside
+a suite, R would be easy to hit while navigating.
+
+It uses the same `netboot_boot_file()` path as the post-update boot, so there
+is one DOL launcher and one set of safety checks rather than two.
+
 ## Self-update over the BBA (Z button)
 
 Press **Z**, then on the host: