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/index.ts

@@ -128,6 +128,10 @@ app.post('/api/games', (req: Request, res) => {
     // starts with nothing released; this list grows as the LLM releases
     // regions and shrinks as they get re-claimed.
     unowned: [],
+    // (v0.23, #16 P4a) No pending nation-op proposals on a fresh game; the
+    // list grows as the LLM proposes renames (and, later, splits/merges) and
+    // shrinks as the player confirms or rejects them.
+    pendingNationOps: [],
   };
   // v0.19 (#16 P1): expand each nation's ISO_A3 country list to the region keys
   // of all its sub-regions, so ownership (and the choropleth) is at region