docs(report): add section 5.3 draft assets

docs/temp-section-5-3-diagrams/README.md

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+# Temporary Section 5.3 Diagrams
+
+These temporary files contain Mermaid diagrams for the `5.3` implementation chapter.
+
+## Files
+
+- [5.3.1 Server Bootstrap](./5.3.1-server-bootstrap.md)
+- [5.3.2 Authentication and Sessions](./5.3.2-authentication-and-sessions.md)
+- [5.3.3 Device Registration and Presence](./5.3.3-device-registration-and-presence.md)
+- [5.3.4 Database Schema and Persistence](./5.3.4-database-schema-and-persistence.md)
+- [5.3.5 Linking and Control Flow](./5.3.5-linking-and-control-flow.md)
+- [5.3.6 Stream Sessions and Signalling](./5.3.6-stream-sessions-and-signalling.md)
+- [5.3.7 Motion Events Notifications Audit](./5.3.7-motion-events-notifications-audit.md)
+- [5.3.8 Recordings and Object Storage](./5.3.8-recordings-and-object-storage.md)
+- [5.3.9 Web Application Implementation](./5.3.9-web-application-implementation.md)
+- [5.3.10 Operational and Support Assets](./5.3.10-operational-and-support-assets.md)
+
+These are temporary working diagrams intended for screenshots and report drafting.