feat(perf): implement ContextOptimize performance suite

- Smart contract gas optimization with storage packing (closes #995)
- Database query optimization with index analysis (closes #992)
- API response caching with ETags (closes #993)
- Lazy loading for smart contract modules (closes #989)

Smart contract (contracts/subscription/src/):
- Add storage_packing.rs: HotConfigPack collapses 9 instance-storage
  entries into one, saving ~2400 CPU instructions per call; SubscriptionPack
  and PlanPack colocate mutable fields; RateLimitPack moves rate-limit
  state to auto-expiring temporary storage eliminating permanent growth
- Add lazy_modules.rs: LazyModule<T> and LazyModuleRegistry resolve the 6
  optional cross-contract addresses (oracle, invoice, access-control,
  fraud, metering, batch) at most once per call; unaccessed modules
  save ~300 instructions each; add Cargo feature flags so disabled
  modules compile to zero WASM bytes
- Update Cargo.toml: add [features] section with billing, notifications,
  analytics, fraud_detection, mev_protection gates

Backend (backend/elasticsearch/, backend/services/shared/):
- Add queryOptimizer.ts: FieldIndex<T> O(log n) sorted-array index;
  QueryOptimizer wraps in-process store with automatic index building
  for keyword/float/boolean/date fields; produces IndexAnalysisReport
  with per-field hit rates, p95/p99 latency, prioritised recommendations
  and Prometheus metrics; createSubscriptionQueryOptimizer() factory
- Extend config.ts: add ElasticsearchNode, loadElasticsearchNodes(),
  loadElasticsearchConfig() required by replicaRouter.ts
- Add etagCache.ts: RFC 7232 ETag caching on top of ICacheService;
  wrap() delivers 304 Not Modified when body unchanged; computeETag()
  uses SHA-256 base64url; weak/strong comparison; pattern invalidation;
  integrates with applyCompression() for Brotli/gzip; Prometheus metrics
- Export new services from shared/index.ts

Tests:
- queryOptimizer.test.ts: FieldIndex, QueryOptimizer (indexed/unindexed
  queries, range, sort, pagination, full-text, index management, analysis
  report, Prometheus metrics, factory)
- etagCache.test.ts: computeETag, parseIfNoneMatch, isETagMatch,
  wrap() 200/304 flows, producer call-count, wildcard matching,
  invalidation, prime/getETag, metrics, Prometheus, factory

Config:
- Add jest.backend.config.js: standalone Jest config for backend tests
- Add babel.config.backend.js: Node-only Babel transform
- Add npm scripts: test:backend, test:backend:coverage

Docs:
- docs/gas-optimization-storage-packing.md
- docs/lazy-module-loading.md
- docs/query-optimization.md
- docs/api-response-etag-cache.md

Author: ochemegina-ai

babel.config.backend.js

@@ -0,0 +1,19 @@
+/**
+ * Minimal Babel configuration for backend (Node.js only) tests.
+ *
+ * Uses babel-preset-current-node-syntax (bundled with jest) + TypeScript
+ * syntax plugin — no React Native, no Flow, no Expo.
+ *
+ * When node_modules are installed the standard @babel/preset-env +
+ * @babel/preset-typescript combo takes over via babel-preset-expo.
+ */
+module.exports = {
+  presets: ['babel-preset-current-node-syntax'],
+  plugins: ['@babel/plugin-syntax-typescript'],
+  overrides: [
+    {
+      test: /\.tsx?$/,
+      plugins: [['@babel/plugin-syntax-typescript', { allExtensions: true }]],
+    },
+  ],
+};