feat: add draw.io Cloudron package (Documentation-Tools)

draw.io (diagrams.net) is a client-side diagramming app. It has no user
model and no server-side state (diagrams live in the browser or cloud
storage), so this is the first package to use the Cloudron
authentication-proxy pattern: httpAuth.type=proxy gates access at the
platform edge — the admin restricts who can reach it and the browser
challenges for Cloudron credentials.

- Wraps the official jgraph/drawio:24.7.17 Tomcat image (pinned, verified)
- No database / no persistent storage; installs curl for the health check
- HTTP port 8080, health check on /
- Validated: docker build + run return HTTP 200, container healthy

Gardening: STATUS/README/JOURNAL updated (8/~57 packaged); new
"official-image wrapper + auth proxy" pattern documented in JOURNAL.

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Assisted-by: Crush:glm-5.2

Package-Workspace/Documentation-Tools/docker-drawio/.env.example

@@ -0,0 +1,14 @@
+# draw.io optional environment variables.
+# The app runs with none of these set; they are tuning knobs only.
+
+# Base URL of the deployment (leave unset to auto-detect).
+# DRAWIO_BASE_URL=
+
+# Run fully self-contained without loading assets from external CDNs.
+# DRAWIO_SELF_CONTAINED=1
+
+# PlantUML server URL for inline UML diagram rendering.
+# PLANTUML_URL=https://www.plantuml.com/plantuml
+
+# draw.io export server URL for server-side PDF/PNG/PDF export.
+# EXPORT_URL=