M-115: re-apply M-113's store-time bswap scoped to the 16-bit GBI-size
family only (PORT_PIXEL16 = bswap16 under #ifdef PORT; PORT_PIXEL32 stays
identity). The fast3d importers disagree on pool byte order:
import_texture_rgba16/_ia16 read manually big-endian bytes, while
import_texture_rgba32 does PD_BE32() on a native load -- M-113's blanket
swap hit both and regressed muzzle flash/ammo HUD (M-114).
Format is the structural discriminator, not compmethod (fire frames span
LOOKUP/RLE/HUFFMANBLUR/RLELOOKUP) or texnum range. Offline census of all
2698 ROM images (scratch/d219_headers.py / d219_census.txt): 94 non-zlib
wide-pixel; the 16-bit family is IMAGE_FIRE_0..14 + texnum 1198-1201/2430/
2510-2523, every ammo/flare/crosshair/muzzle-flash image is RGBA32.
Runtime-verified on Dam (scripted fire): all 15 frames decode format=1,
pool dumps warm R-dominant (mean opaque RGB 255,238,139). RGBA32 pool
bytes bit-identical to the M-114-revert build. User playtest confirmed;
D219 closed. GE_D219RAW probes generalized (no texnum filter), inert.
