Adds deterministic golden fixtures (server/abilities/goldens/) pinning the
EXACT output of buildSystemPrompt (no-tool + tool modes) and buildUserPrompt
for a fixed wwii-1939 preset plus a crafted state that exercises every
optional payload branch (regions, frontier, frontierMilitary, takeoverRisks,
unowned, markers, wars, relations, trades, embargoes, resources, industry).
These are the target: the v0.40.0 modular ability registry (P2-P5) must
reproduce these byte-for-byte. Part of #74.
kamilkrzywda
fc908aaea9