feat(dashboard): header user dropdown (Syncfusion) + proper logout; docs: clarify architecture; build: add splitbuttons; bump alpha.10

Dashboard

Add top-right user dropdown using Syncfusion DropDownButton: shows username + role; menu entries “Profil” and “Abmelden”.
Replace custom dropdown logic with Syncfusion component; position at header’s right edge.
Update /logout page to call backend logout and redirect to /login (reliable user switching).
Build/Config

Add @syncfusion/ej2-react-splitbuttons and @syncfusion/ej2-splitbuttons dependencies.
Update Vite optimizeDeps.include to pre-bundle splitbuttons and avoid import-analysis errors.
Docs

README: Rework Architecture Overview with clearer data flow:
Listener consumes MQTT (discovery/heartbeats) and updates API.
Scheduler reads from API and publishes events via MQTT to clients.
Clients send via MQTT and receive via MQTT.
Worker receives commands directly from API and reports results back (no MQTT).
Explicit note: MariaDB is accessed exclusively by the API Server; Dashboard never talks to DB directly.
README: Add SplitButtons to “Syncfusion Components Used”; add troubleshooting steps for @syncfusion/ej2-react-splitbuttons import issues (optimizeDeps + volume reset).
Copilot instructions: Document header user menu and splitbuttons technical notes (deps, optimizeDeps, dev-container node_modules volume).
Program info

Bump to 2025.1.0-alpha.10 with changelog:
UI: Header user menu (DropDownButton with username/role; Profil/Abmelden).
Frontend: Syncfusion SplitButtons integration + Vite pre-bundling config.
Fix: Added README guidance for splitbuttons import errors.
No breaking changes.

dashboard/vite.config.ts

@@ -19,9 +19,11 @@ export default defineConfig({
     include: [
       '@syncfusion/ej2-react-navigations',
       '@syncfusion/ej2-react-buttons',
+      '@syncfusion/ej2-react-splitbuttons',
       '@syncfusion/ej2-base',
       '@syncfusion/ej2-navigations',
       '@syncfusion/ej2-buttons',
+      '@syncfusion/ej2-splitbuttons',
       '@syncfusion/ej2-react-base',
     ],
     // 🔧 NEU: Force dependency re-optimization