Phase 3e: live texturing + serial receive-latency fixes for the RIO

Texturing (validated live -- game-live-textured.png, the ravine's brown dirt
terrain): the wire model is Division's intensity+ramp scheme. action 26
uploads 8-bit intensity texels ([node][nbytes][w][h] + rows; type 13 =
texture); texmap (12) references the texture; material (11) references its
texmap and a ramp (14: lo/hi RGB); texel color = lerp(lo, hi, i/255). The
backend bakes RGBA per material, uploads to GL, maps with wire UVs
(stride-5: floats 3-4; stride-8/9: floats 6-7).

Serial (directserial fork options, tracked in vpx-device/serialport/):
- rxpollus:<us> -- receive poll tick (stock 1ms); 100us discovers inbound
  bytes ~10x sooner. Validated: sim advanced, camera moved with real RIO.
- rxburst:<n>  -- stock DOSBox re-serializes received bytes at emulated wire
  speed (~1ms/byte at 9600) though they already paid wire time on the real
  cable; a 15-byte analog reply gained ~14ms, blowing the RIO's few-ms ACK
  window and dropping the game into its 15-second retry fallback
  (L4CTRL.CPP limit=15.0 //0.2). rxburst:16 delivers buffered bytes 16x
  faster. game_rio.conf: realport:COM1 rxpollus:100 rxburst:16.

Crash-on-advance fixed: *_TSHD.BGF terrain shadows live only in arena
subdirs the search path misses; null shadow renderable was dereferenced once
the sim moved. All 11 copied into VIDEO/GEO in the working image; game now
runs sustained (560+ frames, textured, no crash). Details in RIO-NOTES.md.

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

emulator/.gitignore

@@ -1,20 +1,21 @@
-# Local working artifacts
-dosbox-x/
-image/
-*.png
-# Phase 3 evidence renders (keep: decoded from the captured VPX stream)
-!divrgb-decoded.png
-!divrgb-frame0.png
-!divrgb-live-gl.png
-!game-cockpit-decoded.png
-!game-mech-decoded.png
-!game-live-gl.png
-dbx_out.txt
-vpx*.txt
-sweep_*.txt
-dbx_err.txt
-src/
-vpxlog.txt
-sent_hex.txt
-build.log
-run_build.sh
+# Local working artifacts
+dosbox-x/
+image/
+*.png
+# Phase 3 evidence renders (keep: decoded from the captured VPX stream)
+!divrgb-decoded.png
+!divrgb-frame0.png
+!divrgb-live-gl.png
+!game-cockpit-decoded.png
+!game-mech-decoded.png
+!game-live-gl.png
+!game-live-textured.png
+dbx_out.txt
+vpx*.txt
+sweep_*.txt
+dbx_err.txt
+src/
+vpxlog.txt
+sent_hex.txt
+build.log
+run_build.sh