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/protocol.test.ts

@@ -4,7 +4,9 @@ import {
   CONQUEST_MILITARY_MARGIN,
   deriveNationResources,
   deriveNationStats,
+  IDEOLOGY_STABILITY_EFFECT,
   migrateRegionStats,
+  nationForPrompt,
   seedRegionStats,
   weightedMedian,
 } from '../shared/protocol';
@@ -337,3 +339,30 @@ describe('canConquer', () => {
     expect(canConquer(49, 50, 0)).toBe(false); // one below → repel
   });
 });
+
+// --- IDEOLOGY_STABILITY_EFFECT (v0.39, #62) ----------------------------------
+
+describe('IDEOLOGY_STABILITY_EFFECT (v0.39.0 #62)', () => {
+  it('a regime shift is a deterministic −5 stability dip', () => {
+    expect(IDEOLOGY_STABILITY_EFFECT).toBe(-5);
+  });
+});
+
+// --- nationForPrompt — ideology (v0.39, #62) ---------------------------------
+
+describe('nationForPrompt — ideology (v0.39.0 #62)', () => {
+  it('stamps the ideology when a nation has one', () => {
+    const n = nation('uk', 'UK', S(50, 50, 50, 50), ['k1']);
+    n.ideology = 'fascism';
+    expect(nationForPrompt(n).ideology).toBe('fascism');
+    // and it survives JSON serialisation (the user prompt path)
+    expect(JSON.stringify(nationForPrompt(n))).toContain('"ideology":"fascism"');
+  });
+
+  it('omits the ideology from the JSON when a nation has none (undefined key dropped)', () => {
+    const n = nation('uk', 'UK', S(50, 50, 50, 50), ['k1']);
+    expect(n.ideology).toBeUndefined();
+    // JSON.stringify drops undefined-valued keys → no "ideology" in the prompt
+    expect(JSON.stringify(nationForPrompt(n))).not.toContain('ideology');
+  });
+});