emulator: in-fork plasma display (serial2=plasma) window in the explode layout

Bring the pod's 128x32 plasma readout in-fork, completing the self-contained
glass cockpit -- no vPLASMA process, no pipe.

- serialplasma.{cpp,h}: CSerialPlasma, a serial<n>=plasma backend that parses
  the game's ESC P graphics stream (L4PLASMA streams whole changed rows;
  receive-only, no replies) into a 128x32 1bpp framebuffer. Transcribed from
  vPLASMA's PlasmaProtocol + VPlasmaDevice (graphics path); the factory
  text-mode/fonts aren't used by the game and aren't rendered, but their escape
  operands are still consumed so the parser can't desync. Seam PLASMA_GetFrame()
  for the renderer.
- vpxlog.cpp: draw the framebuffer as an amber-on-black window in the explode
  layout, lazily created once a plasma port exists, parked centered under the
  lower-left MFD (VPX_PLASMA="x,y,w,h" overrides); WS_EX_NOACTIVATE so it can't
  steal DOSBox focus.
- Register SERIAL_TYPE_PLASMA (serialport.h/.cpp, dosbox.cpp -- documented in
  the vpx-device README step 3d, since those stock files live in the git-ignored
  src tree).
- Confs: serial2 in the _rio confs + deploy templates switches from
  namedpipe pipe:vplasma to the in-fork plasma.

Live-validated 2026-07-24. Real pods keep directserial realport:COM2; the
standalone vPLASMA app keeps namedpipe pipe:vplasma.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

emulator/deploy/net_loop_rio.conf.tmpl

@@ -43,7 +43,7 @@ joysticktype=none
 [serial]
 # in-fork virtual RIO board on COM1 (pad:<n> and inverty are optional args)
 serial1=rio
-serial2=namedpipe pipe:vplasma
+serial2=plasma
 [autoexec]
 mount c "@@ROOT@@\ALPHA_1"
 mount d "@@ROOT@@\net-boot"

emulator/deploy/net_rp_rio.conf.tmpl

@@ -44,7 +44,7 @@ joysticktype=none
 [serial]
 # in-fork virtual RIO board on COM1 (pad:<n> and inverty are optional args)
 serial1=rio
-serial2=namedpipe pipe:vplasma
+serial2=plasma
 [autoexec]
 mount c "@@ROOT@@\ALPHA_1"
 mount d "@@ROOT@@\net-boot"