fix: hide the pad from muxterm on every muos build

muxterm was allowed vendor and product 0001:0001, the id gpio-keys
gives the H700 pad on muOS before 2026-08-28: muxterm and gptokeyb2
both read it and every button acted twice. The allow-list is now
0000:0001, which SDL never reads back for a device (a vendor of 0 makes
a name GUID, read back as 0:0), so a pad plugged in later stays hidden.

- muxterm keeps PgUp and PgDn for its scrollback: in muxterm L1 and R1
  send nothing, and the README and wiki stop promising paging there.
- The offline detection runs with RETROBIOS_INSTALL_OFFLINE=1 instead
  of a closed loopback URL.
- Every launcher sets RETROBIOS_IDLE_EXIT=300 for the interface.
- ROCKNIX: control.ini's -sudokill goes through a sudo stub that runs
  nothing, so the mapper starts with -1.
- The sentinel ends with its launcher, a closed terminal app writes its
  status, a mapper lost mid-run is said and named (gptokeyb2 included),
  and the unwritable-card message stays in view.
- Tests: an SDL GUID model, a gptokeyb2 that outlives its kill, an
  interface that ignores SIGTERM, a zombie, a SIGHUP to the inner run,
  arrow bytes at the question, ROCKNIX's sudo.

wiki/installer.md

@@ -1060,7 +1060,7 @@ muxterm, as the muOS app does.
 | B, Select | Back, and quit on the first screen |
 | X | Tick or untick a system |
 | Y | Options |
-| L1, R1 | Page up, page down |
+| L1, R1 | Page up, page down (not in muxterm, which keeps them for its own scrollback) |
 | Hold Select, then Start | Quit at once (PortMaster port, muOS, Tools) |
 
 Start pressed first also chooses the line in focus: hold Select first. A
@@ -1068,6 +1068,11 @@ running install is then stopped the way B stops it, and the last screen says
 what it wrote. On muOS without PortMaster, muxterm reads the pad itself: Y
 ticks a system, Select shows its keyboard, and Menu quits.
 
+Each launcher also sets `RETROBIOS_IDLE_EXIT` to 300: with no button pressed
+on its first screen for 5 minutes, the interface closes by itself. A pad the
+system has no mapping for sends nothing, and would otherwise leave the
+console stuck on the interface with no way out.
+
 Each launcher tells the interface which buttons reach it, in
 `RETROBIOS_PAD`, so the hints can name them: