Add 5 component data-flow diagrams (Mermaid source + PNG)

- otopcua-dataflow: equipment → drivers (8, with stability tiers) → namespaces → ACL → consumers
- redpanda-eventhub: site ScadaBridge → store-and-forward → central cluster (topics + retention tiers + schema registry) → enterprise consumers
- snowbridge-dataflow: source adapters (Historian/Redpanda) → governed selection + approval workflow → Snowflake landing
- scadabridge-dataflow: OtOpcUa inputs → scripts/templates → multiple outputs (Redpanda, Web APIs, DB, email, equipment writes, Camstar)
- snowflake-dbt-dataflow: landing → staging → curated layer (dim_equipment, fact_state_transitions, mart_oee) → Power BI / AI/ML / ad-hoc

outputs/diagrams/snowbridge-dataflow.mmd

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+flowchart LR
+    subgraph Sources["Data Sources"]
+        HIS["Aveva Historian<br/>(SQL interface)<br/>Year 1 adapter"]
+        RED["Redpanda Topics<br/>(ScadaBridge events)<br/>Year 2 adapter"]
+        FUT["Future Sources<br/>(Ignition, Data Hub, etc.)"]
+    end
+
+    subgraph SnowBridge["SnowBridge (.NET service)"]
+        direction TB
+        SA["Source Adapters<br/>(pluggable per source)"]
+        SEL["Selection Engine<br/>(which tags/topics → Snowflake)"]
+        GOV["Governance Layer"]
+        subgraph Approval["Approval Workflow"]
+            SELF["Self-service<br/>(single tag, non-compliance)"]
+            FOUR["Four-eyes review<br/>(new topic, compliance tier,<br/>high-cost impact)"]
+        end
+        UI["Operator Web UI + API<br/>(RBAC, audit trail,<br/>exportable state)"]
+    end
+
+    subgraph Snowflake["Snowflake"]
+        LAND["Landing Tables<br/>(Snowpipe Streaming<br/>or COPY)"]
+    end
+
+    HIS --> SA
+    RED --> SA
+    FUT -.-> SA
+    SA --> SEL
+    UI --> GOV --> SEL
+    GOV --> Approval
+    SEL --> LAND