Add ScadaBridge topology diagram — clusters, routing, data locality

Shows: central 2-node cluster (South Bend), per-building clusters at
Warsaw campuses, single clusters at smaller sites, hub-and-spoke routing
with optional direct site-to-site, co-location on System Platform nodes.

outputs/diagrams/scadabridge-topology.mmd

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+flowchart TB
+    subgraph Central["Central Cluster (South Bend DC)"]
+        direction LR
+        CN1["Node 1<br/>active"]
+        CN2["Node 2<br/>standby"]
+        CN1 <-->|"Akka.NET<br/>cluster"| CN2
+    end
+
+    subgraph WarsawWest["Warsaw West Campus"]
+        direction TB
+        subgraph WW3["Building 3 Cluster"]
+            WW3N1["Node 1"] <--> WW3N2["Node 2"]
+        end
+        subgraph WW7["Building 7 Cluster"]
+            WW7N1["Node 1"] <--> WW7N2["Node 2"]
+        end
+    end
+
+    subgraph WarsawNorth["Warsaw North Campus"]
+        direction TB
+        subgraph WN1C["Building Cluster"]
+            WNN1["Node 1"] <--> WNN2["Node 2"]
+        end
+    end
+
+    subgraph Shannon["Shannon (single cluster)"]
+        SN1["Node 1"] <--> SN2["Node 2"]
+    end
+
+    subgraph Galway["Galway (single cluster)"]
+        GN1["Node 1"] <--> GN2["Node 2"]
+    end
+
+    subgraph TMT["TMT (single cluster)"]
+        TN1["Node 1"] <--> TN2["Node 2"]
+    end
+
+    subgraph Ponce["Ponce (single cluster)"]
+        PN1["Node 1"] <--> PN2["Node 2"]
+    end
+
+    Central <-->|"hub route"| WarsawWest
+    Central <-->|"hub route"| WarsawNorth
+    Central <-->|"hub route"| Shannon
+    Central <-->|"hub route"| Galway
+    Central <-->|"hub route"| TMT
+    Central <-->|"hub route"| Ponce
+
+    Shannon <-.->|"direct route<br/>(optional)"| Galway
+
+    subgraph Notes["Key: 2-node Akka.NET clusters, co-located on System Platform nodes"]
+        L1["Hub-and-spoke: central routes to all sites"]
+        L2["Direct site-to-site routing available where needed"]
+        L3["Data locality: equipment talks to LOCAL cluster only"]
+    end