refactor: gamedata-driven resolution, drop hardcoded sig/anchors

EncodeField + SendClientMessages now resolve via GameData.GetAddress() from
yappershq.sendproxy.jsonc (single source of truth). Removed the hardcoded
EncodeFieldSig const and the ResolveByString string-anchor lookups from C#.
Added SendClientMessages to gamedata with a makesig-generated sig (rip-relative
lea displacement auto-wildcarded). WriteDeltaEntity deferred to Phase 2 (Ghidra
hasn't linked its format-string xref). Added tools/GhidraStringSig.java
(string-anchor -> function -> makesig). Build clean.

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