feat: port all six scenarios' NPC cast rosters into the data model

Populate cast[] (kind:'npc') for every Continuum scenario, transcribed
from the gm-utility NPC sources — normalising the two schemas (console
{id,name,ess,sec} and module {name,tag,secret}) into
{ id, name, kind, note, secret? }. 57 NPCs total. Pregens/PCs excluded
(separate character-sheet system).

No cast UI consumer yet — the design reserves scenario.cast for a future
cast dashboard, so this is a data-model port guarded by
tests/scenarios/cast.test.js (shape + unique ids). 131 tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/scenarios/cast.test.js

@@ -0,0 +1,27 @@
+import { describe, it, expect } from 'vitest';
+import continuum from '../../src/con/continuum-2026.js';
+import { getScenario } from '../../src/scenarios/index.js';
+
+const scenarios = continuum.slots.map((s) => getScenario(s.scenarioId));
+
+describe('ported cast rosters', () => {
+  it('every Continuum scenario has a non-empty cast', () => {
+    for (const sc of scenarios) {
+      expect(sc.cast.length, sc.meta.id).toBeGreaterThan(0);
+    }
+  });
+
+  it('cast entries are well-formed with unique ids and a valid kind', () => {
+    for (const sc of scenarios) {
+      const ids = sc.cast.map((c) => c.id);
+      expect(new Set(ids).size, sc.meta.id + ' unique ids').toBe(ids.length);
+      for (const c of sc.cast) {
+        expect(typeof c.id, sc.meta.id).toBe('string');
+        expect(c.id.length, sc.meta.id).toBeGreaterThan(0);
+        expect(typeof c.name, sc.meta.id).toBe('string');
+        expect(c.name.length, sc.meta.id).toBeGreaterThan(0);
+        expect(['pc', 'npc'], sc.meta.id + ' ' + c.id).toContain(c.kind);
+      }
+    }
+  });
+});