A third region state (contested frontline): a region in no nation's territory and not in unowned, opened/resolved by the LLM, tied to an active war. Sole-ownership invariant preserved. Durable GameState.contested; contested-inert stub; map legend stays at 7.
Adds the sea ability: a fixed set of 12 named sea zones with sole-control
semantics, contest-by-higher-military, and a deterministic per-turn
+1 military/+1 economy bonus for each claimed zone. Durable (owns
GameState.seaZones), additive migration, stub-inert (e2e unaffected).
Fixes#65
Design note: Gitea #65 sketched a free-form 'naval' layer; the implemented
approved design is this richer 'sea' layer with a fixed zone set.
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.