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-InboundAPI.md

@@ -123,20 +123,8 @@ API method scripts are compiled at central startup — all method definitions ar
 
 ## Request Flow
 
-```
-External System
-    │
-    ▼
-Inbound API (Central)
-    ├── 1. Extract API key from request
-    ├── 2. Validate key exists and is enabled
-    ├── 3. Resolve method by name
-    ├── 4. Check API key is in method's approved list
-    ├── 5. Validate and deserialize parameters
-    ├── 6. Execute implementation script (subject to method timeout)
-    ├── 7. Serialize return value
-    └── 8. Return response
-```
+![inboundapi-request-flow](diagrams/inboundapi-request-flow.png)
+<!-- source: diagrams/inboundapi-request-flow.drawio — edit, then re-export with export-drawio.sh -->
 
 ## Implementation Script Capabilities