D88.4: propDefs record format spec + N64->PC converter (d88_propdefs.py)

The propDefs stream is a flat s32[]; each record's serialized N64 word count
is fixed across all 21 levels (verified: the getools C sources tile every
propDefs region byte-for-byte against the ROM). Every pointer member is 0 in
the file, so records containing pointers grow 4->8B per pointer on PC.

d88_propdefs.py rewrites each record to its native PC struct layout: header
word (u16+u8+u8) and _mkword half-pairs swapped independently, scalars
bswap32'd, pointer slots widened to 8 zero bytes, runtime areas zero-filled.
d88_layoutprobe.c (expanded) is the compiler-verified sizeof/offsetof source
for PROPDEF_PC_BYTES. Converts + walk-verifies all 21 levels clean.

.gitignore

@@ -1,6 +1,6 @@
 #Git and VS files
 .*~
-__pycache__/*
+__pycache__/
 .vscode/
 .[vV][sS]/