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/types.ts

@@ -249,6 +249,23 @@ export interface IndustryProject {
   type: IndustryType;
 }
 
+/**
+ * (v0.43.0, #65) One sea-zone claim: which nation controls one of the fixed
+ * sea zones (see `SEA_ZONES` in `shared/protocol.ts`). The world keeps at
+ * most ONE claim per zone — a new op on an already-claimed zone REPLACES the
+ * controller in place (the zone's entry is updated, never duplicated), and if
+ * a turn declares the same zone for two different resolved nations the higher
+ * current `stats.military` wins (a tie: the op listed earlier in the turn's
+ * `control` array). Sea control is fully parallel to but INDEPENDENT of land:
+ * it never touches `territory` / `unowned`.
+ */
+export interface SeaZoneClaim {
+  /** The sea zone (one of `SEA_ZONE_IDS`). */
+  zone: string;
+  /** The id of the nation that controls it (resolved, not a name). */
+  by: string;
+}
+
 /**
  * (v0.33.0, #56) A first-class **war** — a named, ongoing armed conflict
  * between two or more nations. Unlike the boolean `war` relation (which a
@@ -443,6 +460,20 @@ export interface GameState {
    * with this defaulted to `[]` (see server/db.ts) — additive, no data wipe.
    */
   industry: IndustryProject[];
+  /**
+   * (v0.43.0, #65) Sea-zone control (see {@link SeaZoneClaim}): one entry per
+   * controlled sea zone — which of the 12 fixed zones (`SEA_ZONES`) each
+   * nation controls. At most ONE entry per zone (unique by `zone`); a turn's
+   * `sea.control` ops upsert entries (a re-claim by a different nation
+   * replaces the controller in place; a same-zone contest goes to the higher
+   * current `stats.military`, a tie to the earlier-listed op). Every
+   * committed turn each claim's controller earns a small deterministic
+   * military/economy bonus (`SEA_ZONE_BONUS`). Sea control never moves land
+   * (`territory` / `unowned` are untouched). Always `[]` on a fresh game;
+   * rows saved before v0.43 load with this defaulted to `[]` (see
+   * server/db.ts) — additive, no data wipe.
+   */
+  seaZones: SeaZoneClaim[];
 }
 
 /**