feat: #65 sea control — 11th ability (v0.43.0)

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.

server/stub.ts

@@ -100,6 +100,14 @@ export interface StubPayload {
    * deterministicTurn), so the industry path is covered by unit tests only.
    */
   industry?: Array<{ regionKey: string; type: string }>;
+  /**
+   * (v0.43.0, #65) The currently active sea-zone control
+   * (`{ zone, by }` — fixed sea-zone id + controlling nation id), emitted by
+   * the engine's user prompt (always, even when empty). The stub ignores this
+   * field — it never claims, contests or re-claims a sea zone (see
+   * deterministicTurn), so the sea path is covered by unit tests only.
+   */
+  seaZones?: Array<{ zone: string; by: string }>;
 }
 
 function truncate(s: string, n: number): string {
@@ -173,6 +181,18 @@ function truncate(s: string, n: number): string {
  * (v0.39.0, #62) The stub likewise NEVER changes a nation's ideology (it
  * always returns `ideology: { changes: [] }`) — the ideology path is covered
  * by unit tests only, keeping the e2e assertions untouched.
+ *
+ * (v0.41.0, #63) The stub likewise NEVER declares a disaster or pandemic (it
+ * always returns `disasters: { events: [] }`) — the disasters path is covered
+ * by unit tests only, keeping the e2e assertions untouched.
+ *
+ * (v0.42.0, #64) The stub likewise NEVER declares a migration / refugee flow
+ * (it always returns `migration: { ops: [] }`) — the migration path is
+ * covered by unit tests only, keeping the e2e assertions untouched.
+ *
+ * (v0.43.0, #65) The stub likewise NEVER claims, contests or re-claims a sea
+ * zone (it always returns `sea: { control: [] }`) — the sea-control path is
+ * covered by unit tests only, keeping the e2e assertions untouched.
  */
 export function deterministicTurn(p: StubPayload): TurnResult {
   const state = p.state;
@@ -252,13 +272,13 @@ export function deterministicTurn(p: StubPayload): TurnResult {
     nationOps: [], // the stub never proposes nation ops (see doc comment)
   };
 
-  // The 9 ability fields, filled by the registry in its canonical order. The
+  // The 11 ability fields, filled by the registry in its canonical order. The
   // stub is ability-inert: every ability contributes its own no-op default
   // (each ability's `stub()` — see the per-ability doc comments above), so the
   // e2e assertions are unaffected. The insertion order here (ABILITIES) is the
   // historical key order pinned by the stub's deterministic output
   // (takeovers → wars → hybrid → economy → industry → nuclear → leaders →
-  // ideology → disasters), which must stay byte-identical.
+  // ideology → disasters → migration → sea), which must stay byte-identical.
   const abilities = {} as Record<AbilityField, unknown>;
   for (const a of ABILITIES) abilities[a.field] = a.stub();