Phase 8: Production readiness — failover tests, security hardening, sandboxing, deployment docs

- WP-1-3: Central/site failover + dual-node recovery tests (17 tests)
- WP-4: Performance testing framework for target scale (7 tests)
- WP-5: Security hardening (LDAPS, JWT key length, no secrets in logs) (11 tests)
- WP-6: Script sandboxing adversarial tests (28 tests, all forbidden APIs)
- WP-7: Recovery drill test scaffolds (5 tests)
- WP-8: Observability validation (structured logs, correlation IDs, metrics) (6 tests)
- WP-9: Message contract compatibility (forward/backward compat) (18 tests)
- WP-10: Deployment packaging (installation guide, production checklist, topology)
- WP-11: Operational runbooks (failover, troubleshooting, maintenance)
92 new tests, all passing. Zero warnings.

src/ScadaLink.ExternalSystemGateway/ExternalSystemGatewayOptions.cs

@@ -0,0 +1,13 @@
+namespace ScadaLink.ExternalSystemGateway;
+
+/// <summary>
+/// Configuration options for the External System Gateway component.
+/// </summary>
+public class ExternalSystemGatewayOptions
+{
+    /// <summary>Default HTTP request timeout per external system call.</summary>
+    public TimeSpan DefaultHttpTimeout { get; set; } = TimeSpan.FromSeconds(30);
+
+    /// <summary>Maximum number of concurrent HTTP connections per external system.</summary>
+    public int MaxConcurrentConnectionsPerSystem { get; set; } = 10;
+}