Nation-op proposals (P4a, #16): protocol types, pendingNationOps state, engine propose/resolve (stage 1)

- shared/protocol.ts: RenameOp/SplitOp/MergeOp + NationOp union; TurnResult.nationOps (required); ConfirmNationOp/RejectNationOp request+response types
- shared/types.ts: GameState.pendingNationOps (type-only import of NationOp — no runtime cycle)
- server/engine.ts: validateNationOps parser wired into validateTurnResult; isMeaningful counts proposals; applyTurnResult appends to the surviving pending list (never applies); runTurn fallback literal; system prompt gains the nationOps JSON field + rename proposal rule (both modes); new resolveNationRef/applyNationOp/confirmNationOp/rejectNationOp (id-first then unique case-insensitive name; rename changes Nation.name only; split/merge no-op until P4b; index validation returns null for 400)
- server/db.ts: legacy rows load with pendingNationOps defaulted to []
- server/index.ts: fresh games start with pendingNationOps: []
- server/stub.ts: deterministicTurn returns nationOps: [] (the stub never proposes — unit-only coverage, matching P3)
- tests: fixture updates (engine/db/map/regions) + new suites for resolveNationRef, validateNationOps, proposal lifecycle, confirm/reject (151 tests total)

server/stub.ts

@@ -57,6 +57,10 @@ function truncate(s: string, n: number): string {
  * always returns `unowned: []`) — e2e assertions rely on its fully-deterministic
  * one-conquest behavior, so the release/re-claim path is exercised by unit
  * tests only (see server/engine.test.ts).
+ *
+ * (v0.23, #16 P4a) The stub likewise NEVER proposes nation-management ops (it
+ * always returns `nationOps: []`) — the propose→confirm/reject flow is
+ * covered by unit tests only, keeping the e2e assertions untouched.
  */
 export function deterministicTurn(p: StubPayload): TurnResult {
   const state = p.state;
@@ -121,6 +125,7 @@ export function deterministicTurn(p: StubPayload): TurnResult {
     relations: otherId ? [{ a: pid, b: otherId, set: 'ally' }] : [],
     territoryChanges,
     unowned: [], // the stub never creates no man's land (see doc comment)
+    nationOps: [], // the stub never proposes nation ops (see doc comment)
   };
 }