feat(#56): War as a first-class state — declare/end ops, mutual-defense drag-in, relation sync

Promote the bare 'war' relation to a named War entity in GameState.wars:
- War: { id, sides[], declaredTurn, declaredDate?, aims?, status, front? }
- TurnResult.wars: { declare: WarDeclareOp[], end: WarEndOp[] }
- syncWarRelations: derive 'war' from active wars, fallback to 'hostile' on end
- Mutual-defense drag-in: belligerent allies added to sides (one level)
- Bare 'war' back-compat: never downgraded, never force-created
- Stub: empty wars (e2e unaffected); ~30 new unit tests

v0.33.0

server/db.ts

@@ -49,6 +49,10 @@ export function openDb(filePath: string): Db {
         if (state.pendingNationOps === undefined) state.pendingNationOps = [];
         // (v0.27, #44) Same for map markers: a legacy game has none placed.
         if (state.markers === undefined) state.markers = [];
+        // (v0.33.0, #56) Same for named wars: a legacy game has none declared
+        // (any pre-v0.33 `war` relation stays a bare/implicit relation — see
+        // syncWarRelations, which never force-creates a War entity).
+        if (state.wars === undefined) state.wars = [];
         // (v0.28, #46) Rows saved before per-region stats existed are migrated
         // ONCE at load time (and never re-migrated afterwards — the field is
         // then present): each owned region is seeded with a copy of its owner's