feat(#62): ideology / government-type change (v0.39.0)

Add a per-nation free-form ideology (form of government) field and a
TurnResult.ideology lever (coups / revolutions / reforms / constitutional
changes) with a deterministic -5 stability dip and political narration.

- shared/types.ts: Nation.ideology?: string (optional/additive)
- shared/protocol.ts: IdeologyChange / IdeologyOps, IDEOLOGY_STABILITY_EFFECT
  = -5, TurnResult.ideology (required, between leaders and markers),
  nationForPrompt now carries ideology
- server/engine.ts: validateIdeologyOps (exported, never throws),
  applyIdeologyChange (resolve -> set field -> -5 dip mirrored to regions +
  re-derived -> political event), ideology block in applyTurnResult after
  leaders / before markers, isMeaningful + validateTurnResult + system prompt
  + runTurn unclear fallback
- server/stub.ts: StubPayload gains ideology; deterministicTurn returns
  ideology: { changes: [] } (never changes one, e2e unaffected)
- Tests: engine.test.ts (validate / isMeaningful / applyTurnResult /
  buildUserPrompt), protocol.test.ts (constant + nationForPrompt),
  db.test.ts (legacy load + round-trip); every TurnResult fixture updated
- package.json -> 0.39.0; CHANGELOG v0.39.0 entry

server/stub.ts

@@ -19,6 +19,9 @@ export interface StubPayload {
     // `leader` (v0.38.0, #61) is the per-nation named leader stamped by the
     // engine; the stub ignores it — it never changes a leader (see
     // deterministicTurn).
+    // `ideology` (v0.39.0, #62) is the per-nation form of government stamped
+    // by the engine; the stub ignores it — it never changes an ideology (see
+    // deterministicTurn).
     nations: Record<
       string,
       {
@@ -26,6 +29,7 @@ export interface StubPayload {
         territory?: string[];
         nuclear?: boolean;
         leader?: { name: string };
+        ideology?: string;
       }
     >;
   };
@@ -160,6 +164,14 @@ function truncate(s: string, n: number): string {
  * strike (it always returns `nuclear: { arm: [], strikes: [] }`) — the
  * nuclear / WMD path is covered by unit tests only, keeping the e2e
  * assertions untouched.
+ *
+ * (v0.38.0, #61) The stub likewise NEVER changes a leader (it always returns
+ * `leaders: { changes: [] }`) — the leader path is covered by unit tests
+ * only, keeping the e2e assertions untouched.
+ *
+ * (v0.39.0, #62) The stub likewise NEVER changes a nation's ideology (it
+ * always returns `ideology: { changes: [] }`) — the ideology path is covered
+ * by unit tests only, keeping the e2e assertions untouched.
  */
 export function deterministicTurn(p: StubPayload): TurnResult {
   const state = p.state;
@@ -233,6 +245,7 @@ export function deterministicTurn(p: StubPayload): TurnResult {
     industry: { projects: [] }, // the stub never declares industry projects (see doc comment)
     nuclear: { arm: [], strikes: [] }, // the stub never arms or strikes (see doc comment)
     leaders: { changes: [] }, // the stub never changes leaders (see doc comment)
+    ideology: { changes: [] }, // the stub never changes ideologies (see doc comment)
     markers: { add: [], remove: [] }, // the stub never touches markers (see doc comment)
   };
 }