feat: license export compatible with NetBox-SLM

When the netbox_slm plugin is installed, the "Lizenzen" section reads
its SoftwareLicense objects automatically:

- Scope matching via installations on devices, VMs or clusters in the
  exported site/location/tenant, plus licenses assigned to the tenant
  and tenant-less licenses of its tenant group (incl. parent groups) or,
  for tenant group exports, of the group and its subgroups.
- One table per manufacturer: license, product/version, type, amount,
  validity incl. renewal interval, status (active, expires in N days,
  expired, lifetime), support, installation target and tenant.
- License keys only with the "include secrets" option.
- Other configured license_sources keep working alongside.

Table cells in HTML/PDF now preserve line breaks.

Bump version to 0.9.0.

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 = "0.8.0"
+    version = "0.9.0"
     author = "Claude"
     base_url = "customer-export"
     min_version = "4.6.8"