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.

shared/protocol.ts

@@ -707,6 +707,82 @@ export interface MigrationOps {
   ops: MigrationOp[];
 }
 
+// ---------------------------------------------------------------------------
+// (v0.43.0, #65) Sea zones & sea control — the naval layer, fully parallel to
+// but INDEPENDENT of land. The world has a fixed set of 12 named SEA ZONES
+// ({@link SEA_ZONES}); each is under the SOLE CONTROL of at most one nation.
+// Controlling a sea zone never moves land (`territory` / `unowned` are
+// untouched) and moving land never touches a sea zone. `SeaZoneClaim` (the
+// durable per-zone record, `{ zone, by }`) lives in `shared/types.ts` like
+// `Trade` / `Embargo` / `War` / `IndustryProject`; `GameState.seaZones` is a
+// list of them, unique per zone (`[]` at creation; a legacy SQLite row
+// without the field loads as `[]` — additive, never wiped). Each turn the LLM
+// declares `TurnResult.sea.control` ops — one op names the zone and the
+// nation that (now) controls it. The engine resolves `by` (id first, then a
+// case-insensitive unique name) and UPSERTS the zone's claim (replace in
+// place if the zone is already claimed, append if new). If two or more ops
+// this turn claim the SAME zone for DIFFERENT resolved nations, the zone is
+// CONTESTED: the higher current `stats.military` wins (a tie goes to the op
+// listed earlier in the `control` array) — deterministic, no hidden
+// randomness; an unresolvable `by` is dropped (never thrown). Every committed
+// turn — including a turn with an empty `control` — each existing claim's
+// controller earns a small DETERMINISTIC bonus (`SEA_ZONE_BONUS = 1` military
+// + 1 economy, clamped to 0–100, mirrored to the controller's regions and
+// re-derived with the same 0-region / no-entry guards as the economy /
+// migration layers); a claim whose nation no longer exists is skipped (the
+// claim is kept, never thrown). The layer is DURABLE (unlike the turn-
+// transient hybrid / disasters / migration layers): `GameState.seaZones`
+// persists across turns and in SQLite. The user payload carries the current
+// `seaZones` list so the model knows who controls which zone.
+
+/** The 12 named sea zones the world model knows (v0.43.0, #65). */
+export const SEA_ZONES = [
+  { id: 'north-atlantic', name: 'North Atlantic' },
+  { id: 'south-atlantic', name: 'South Atlantic' },
+  { id: 'pacific', name: 'Pacific Ocean' },
+  { id: 'indian', name: 'Indian Ocean' },
+  { id: 'mediterranean', name: 'Mediterranean Sea' },
+  { id: 'north-sea', name: 'North Sea' },
+  { id: 'baltic', name: 'Baltic Sea' },
+  { id: 'arctic', name: 'Arctic Ocean' },
+  { id: 'black-sea', name: 'Black Sea' },
+  { id: 'gulf-mexico', name: 'Gulf of Mexico' },
+  { id: 'red-sea', name: 'Red Sea' },
+  { id: 'sargasso', name: 'Sargasso Sea' },
+] as const;
+
+/** The set of valid sea-zone ids (v0.43.0, #65). */
+export const SEA_ZONE_IDS: ReadonlySet<string> = new Set(SEA_ZONES.map((z) => z.id));
+
+/** Whether `id` is one of the fixed sea-zone ids (v0.43.0, #65). */
+export function isSeaZoneId(id: string): boolean {
+  return SEA_ZONE_IDS.has(id);
+}
+
+/** The display name of a sea-zone id; an unknown id is returned as-is (v0.43.0, #65). */
+export function seaZoneName(id: string): string {
+  return SEA_ZONES.find((z) => z.id === id)?.name ?? id;
+}
+
+/**
+ * A single sea-control op (v0.43.0, #65): `zone` is one of the fixed
+ * {@link SEA_ZONES} ids and `by` is the nation that (now) controls it (by id
+ * or name). One op SETS or REPLACES the zone's controller; two or more ops on
+ * the same zone for different nations are CONTESTED — the higher current
+ * `stats.military` wins (a tie: the earlier-listed op).
+ */
+export interface SeaControlOp {
+  /** The sea zone (one of {@link SEA_ZONE_IDS}). */
+  zone: string;
+  /** The controlling nation (by id or name). */
+  by: string;
+}
+
+/** The sea-control block of a `TurnResult`. Required; default `{ control: [] }`. */
+export interface SeaOps {
+  control: SeaControlOp[];
+}
+
 /** The exact JSON object the world-simulator LLM must return for a turn. */
 export interface TurnResult {
   date: string;
@@ -899,6 +975,23 @@ export interface TurnResult {
    * `{ ops: [] }`.
    */
   migration: MigrationOps;
+  /**
+   * (v0.43.0, #65) Sea-zone control ops this turn — the naval layer, fully
+   * parallel to but INDEPENDENT of land: each op names one of the 12 fixed
+   * sea zones (`SEA_ZONES`) and the nation that now controls it. The engine
+   * resolves `by` (id first, then a case-insensitive unique name) and
+   * upserts the zone's claim in `GameState.seaZones` (a single op sets or
+   * replaces the controller; two or more ops on the same zone for different
+   * nations are CONTESTED — the higher current `stats.military` wins, a tie
+   * goes to the op listed earlier in `control`; an unresolvable `by` is
+   * dropped, never thrown). Every committed turn, each existing claim's
+   * controller earns a small deterministic military/economy bonus
+   * (`SEA_ZONE_BONUS`). Sea control never moves land: `territory` and
+   * `unowned` are untouched. At most 1–2 per turn, each narrated in `events`
+   * (a `military` or `diplomatic` event). Required; default
+   * `{ control: [] }`.
+   */
+  sea: SeaOps;
   /**
    * (v0.27, #44) Map-marker ops this turn. `add` places new named markers
    * (the engine positions each at its region's centroid + a small