test: Add end-to-end smoke tests (Agent 99)

- Create comprehensive smoke test suite for post-deployment validation
- Implement 4 test categories: infrastructure, service, authentication, order flow
- Add graceful failure handling for unavailable services
- Create automated test runner script with multiple modes (fast, verbose, category)
- Document known blockers from Agent 96 (Backtesting/ML services)
- Add 30+ individual smoke tests covering critical paths
- Enable smoke-tests feature in tests/Cargo.toml
- Create detailed README with usage and troubleshooting

Test Categories:
1. Infrastructure Health: PostgreSQL, Redis, Vault, InfluxDB, Prometheus, Grafana
2. Service Health: Trading Service, API Gateway (+ blocked: Backtesting, ML)
3. Authentication Flow: JWT, sessions, revocation, rate limiting
4. Basic Order Flow: Order CRUD, positions, order history

Features:
- Configurable timeouts (5-10s per test)
- Environment variable configuration
- Graceful service unavailability handling
- Parallel and sequential execution modes
- Detailed pass/fail reporting

Usage:
  ./run_smoke_tests.sh              # Run all tests
  ./run_smoke_tests.sh --fast       # Critical tests only
  ./run_smoke_tests.sh --verbose    # Debug logging
  ./run_smoke_tests.sh --category infrastructure

Blocked Tests (marked with #[ignore]):
- Backtesting Service (config issues from Agent 96)
- ML Training Service (config issues from Agent 96)

Wave 125 Phase 3B - Deployment Excellence

Cargo.lock

@@ -9000,6 +9000,7 @@ dependencies = [
  "hdrhistogram",
  "influxdb2",
  "jemalloc_pprof",
+ "jsonwebtoken",
  "lazy_static",
  "ml",
  "num 0.4.3",
@@ -9010,6 +9011,7 @@ dependencies = [
  "rand 0.8.5",
  "rand_distr 0.4.3",
  "redis",
+ "reqwest 0.12.23",
  "risk",
  "risk-data",
  "rstest 0.22.0",
@@ -9027,6 +9029,7 @@ dependencies = [
  "tokio-test",
  "toml",
  "tonic",
+ "tonic-health",
  "tracing",
  "tracing-subscriber",
  "trading_engine",