Phase 0 WP-0.10–0.12: Host skeleton, options classes, sample configs, and execution framework

- WP-0.10: Role-based Host startup (Central=WebApplication, Site=generic Host),
  15 component AddXxx() extension methods, MapCentralUI/MapInboundAPI stubs
- WP-0.11: 12 per-component options classes with config binding
- WP-0.12: Sample appsettings for central and site topologies
- Add execution procedure and checklist template to generate_plans.md
- Add phase-0-checklist.md for execution tracking
- Resolve all 21 open questions from plan generation
- Update IDataConnection with batch ops and IAsyncDisposable
57 tests pass, zero warnings.

src/ScadaLink.Host/appsettings.Site.json

@@ -0,0 +1,53 @@
+{
+  "ScadaLink": {
+    "Node": {
+      "Role": "Site",
+      "NodeHostname": "site-a-node1",
+      "SiteId": "SiteA",
+      "RemotingPort": 8082
+    },
+    "Cluster": {
+      "SeedNodes": [
+        "akka.tcp://scadalink@site-a-node1:8082",
+        "akka.tcp://scadalink@site-a-node2:8082"
+      ],
+      "SplitBrainResolverStrategy": "keep-oldest",
+      "StableAfter": "00:00:15",
+      "HeartbeatInterval": "00:00:02",
+      "FailureDetectionThreshold": "00:00:10",
+      "MinNrOfMembers": 1
+    },
+    "Database": {
+      "SiteDbPath": "./data/scadalink.db"
+    },
+    "DataConnection": {
+      "ReconnectInterval": "00:00:05",
+      "TagResolutionRetryInterval": "00:00:10",
+      "WriteTimeout": "00:00:30"
+    },
+    "StoreAndForward": {
+      "SqliteDbPath": "./data/store-and-forward.db",
+      "ReplicationEnabled": true
+    },
+    "Communication": {
+      "DeploymentTimeout": "00:02:00",
+      "LifecycleTimeout": "00:00:30",
+      "QueryTimeout": "00:00:30",
+      "TransportHeartbeatInterval": "00:00:05",
+      "TransportFailureThreshold": "00:00:15"
+    },
+    "HealthMonitoring": {
+      "ReportInterval": "00:00:30",
+      "OfflineTimeout": "00:01:00"
+    },
+    "SiteEventLog": {
+      "RetentionDays": 30,
+      "MaxStorageMb": 1024,
+      "PurgeScheduleCron": "0 2 * * *"
+    },
+    "Notification": {},
+    "Logging": {
+      "MinimumLevel": "Information"
+    }
+  }
+}