refactor: table-driven encoder classification (offset-resolved registry) + fixed32/64

Classify now reads the 8-bucket encoder registry at runtime instead of hardcoded
per-encoder identity sigs. One gamedata entry resolves the table:
EncoderRegistry sig (table-load lea) + factory '+3 r' (skip opcode -> rip-resolve
-> 0x45f360). BuildEncoderTypeMap walks 8 buckets x {handler,count}, entries at
0x80 stride (name@+0, fn@+0x30), maps fn->FieldType by (bucket,name). Removed
EncodeUInt32/Float32/Bool identity sigs. Added Fixed32 (raw32) + Fixed64 (2x32)
write handlers. Auto-covers all registry types; unknown->passthrough. Build 0/0.

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