feat: optional device images in rack elevations, HTML preview in new tab

- New export option "Gerätebilder anzeigen": the SVG is rendered with
  include_images and the /media/ image links are replaced by embedded
  data URIs, since Word, WeasyPrint and SVG-as-image cannot load
  login-protected files. The Pillow PNG renderer draws the front/rear
  images too, with the device name on a dark label.
- Custom rack_svg_renderer adapters receive images=..., older adapters
  without that parameter keep working.
- The HTML preview now opens in a new browser tab.

Bump version to 0.3.0.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

netbox_customer_export/__init__.py

@@ -5,7 +5,7 @@ class CustomerExportConfig(PluginConfig):
     name = "netbox_customer_export"
     verbose_name = "Kunden-Export"
     description = "Kundendokumentation als PDF oder Word exportieren"
-    version = "0.2.0"
+    version = "0.3.0"
     author = "Claude"
     base_url = "customer-export"
     min_version = "4.6.8"