Adds server/abilities/registry.test.ts, the safety net for the refactor:
- GOLDEN PROMPTS: the refactored engine's system prompt (both tool
variants) and user prompt are asserted BYTE-IDENTICAL to the committed
fixtures in server/abilities/goldens/ (captured in P1 from the
pre-refactor engine). The state builder the goldens were captured from
is re-embedded here, with a REGEN_GOLDENS=1 mode to rewrite the
fixtures after an intentional prompt change (verified a no-op — the
refactored output is exactly stable).
- REGISTRY CONTRACT: ABILITIES is the canonical 8-ability order with 8
distinct TurnResult fields; each ability's default() equals the
canonical TurnResult default and is a FRESH value (never a shared
reference); the default is never "meaningful" while a populated value
is; the registry declares exactly the durable GameState fields the db
migration must default (wars/trades/embargoes/industry); the registry
composes (a hypothetical extra ability appends cleanly to every
uniform loop); and the engine still re-exports every name its callers
import from it (backward compatibility).
The throwaway _golden-capture.ts is deleted (its logic is now the
REGEN mode of this test).
Fixes#74
