Initial commit: epaper-dashboard for 7.3" ACeP 7-Color display

- dashboard.py: plugin-based renderer with 4x4 grid layout
- admin.py: web UI with layout editor + plugin configs
- layout.py: pack algorithm, item placement, grid system
- plugins/: clock, weather, system, spotify, strava, gmail, minimax, hello
- network_watchdog.py: WiFi AP/client mode management
- waveshare_epd_init.py: vendor driver stub

.env.example

@@ -0,0 +1,4 @@
+# Admin-UI Credentials. Default im Code ist admin/admin — bitte ändern!
+# Nach dem Ändern: admin.py neu starten.
+EPAPER_ADMIN_USER=admin
+EPAPER_ADMIN_PASSWORD=admin