fix(simulation): add TypeScript types for simulation pipeline + remove dead legacy fallbacks (#2414)

- Add scripts/seed-forecasts.types.d.ts with ambient interfaces for all
  simulation data structures (CandidatePacket, TheaterResult, SimulationOutcome,
  ExpandedPath, SimulationEvidence, SimulationAdjustmentDetail)
- Add // @ts-check + @param JSDoc to contradictsPremise, negatesDisruption,
  computeSimulationAdjustment, applySimulationMerge
- Add scripts/jsconfig.json to enable tsc --checkJs on seed-forecasts.mjs
- Remove dead legacy fallbacks candidatePacket?.topBucketId and
  candidatePacket?.topChannel (these fields were never at top level in
  production; the correct path is candidatePacket.marketContext.topBucketId).
  TypeScript now enforces this at write time.
- Update all test fixtures to use marketContext: { topBucketId, topChannel }
  shape, matching production CandidatePacket structure

scripts/jsconfig.json

@@ -0,0 +1,15 @@
+{
+  "compilerOptions": {
+    "checkJs": true,
+    "strict": false,
+    "noImplicitAny": false,
+    "target": "ES2022",
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "allowJs": true,
+    "maxNodeModuleJsDepth": 0,
+    "skipLibCheck": true
+  },
+  "include": ["seed-forecasts.mjs", "seed-forecasts.types.d.ts"],
+  "exclude": []
+}