docs: render architecture & flow diagrams as draw.io charts

Replace ASCII-art diagrams across the README and docs/ with editable
.drawio sources plus exported PNGs, so the diagrams render clearly in
rendered markdown and can be maintained/regenerated instead of being
hand-edited as fragile text art. Non-diagram blocks (code, folder
trees, UI wireframes) were left as text.

docs/requirements/Component-SiteRuntime.md

@@ -27,21 +27,8 @@ Site clusters only.
 
 ## Actor Hierarchy
 
-```
-Deployment Manager Singleton (Cluster Singleton)
-├── Instance Actor ("MachineA-001")
-│   ├── Script Actor ("MonitorSpeed") — coordinator
-│   │   └── Script Execution Actor — short-lived, per invocation
-│   ├── Script Actor ("CalculateOEE") — coordinator
-│   │   └── Script Execution Actor — short-lived, per invocation
-│   ├── Alarm Actor ("OverTemp") — coordinator (computed)
-│   │   └── Alarm Execution Actor — short-lived, per on-trigger invocation
-│   ├── Alarm Actor ("LowPressure") — coordinator (computed)
-│   └── Native Alarm Actor ("OpcUaServer1") — read-only mirror, peer to Alarm Actor
-├── Instance Actor ("MachineA-002")
-│   └── ...
-└── ...
-```
+![siteruntime-actor-hierarchy](diagrams/siteruntime-actor-hierarchy.png)
+<!-- source: diagrams/siteruntime-actor-hierarchy.drawio — edit, then re-export with export-drawio.sh -->
 
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