fix(gamedata): use ModSharp schema (Addresses/refs), not SourceMod 'Signatures'

GameData.Register threw 'No valid gamedata for platform linux' because the
top-level key was 'Signatures' (a SourceMod-ism). ModSharp's schema uses
Addresses/Offsets/VFuncs with per-entry { library, linux/windows sig, refs }.
Moved EncodeField under Addresses and added the string-anchor ref
('EncodeField encoder wrote %d bits') as an update-robust fallback alongside
the verified byte sig. Records the dynamic gdb confirmation (rsi=0 => shared
encode, fires per field).

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