dsda-doom: wrong colours, silent sound lumps, black GL textures (2026-10-16/17)

Symptom. The first smoke at 1920x1080 in software ran at about 5 fps; at 960x540 the frame came out in wrong colours, green-tinted through SDL’s GL renderer (batch 2026-10-16-dsda-doom-software). The engine’s own sound lumps didn’t play right, screenshots had the wrong byte order, and the GL renderer drew walls, sprites and menus missing or black.

Cause. Three big-endian assumptions and one missing GL feature:

• dsda-doom.wad’s DMX sound lumps are little-endian and were read in host order;
• the software renderer’s SDL buffer wasn’t in the texture’s own format, so the pixel words were read with their bytes the wrong way round; screenshots likewise;
• the GL renderer uploads every indexed texture as GL_RG, and nv30 has no ARB_texture_rg.

Fix. 0001 reads the DMX lumps little-endian; 0003 puts the software renderer’s SDL buffer in the texture’s own format (+ps3.231, batch 2026-10-16-dsda-doom-colours); 0004 writes screenshots as RGB24; 0002 uploads the indexed textures as GL_LUMINANCE_ALPHA (+ps3.247: the GL renderer runs, 48.8 fps on the GL timedemo, batch 2026-10-17-dsda-doom-gl-music). The software renderer then gave 33 fps with the demo unfinished on Mesa ps3.246 and 38 finished on ps3.262.