Bump @einfach-produktiv/invoicing to 0.2.6 (embedded-font fix)

Picks up the Liberation Sans font-embedding fix for PDF/A-3 compliance
— fixes invoice PDF downloads/emails generated by this app.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

package-lock.json

@@ -455,8 +455,8 @@
       }
     },
     "node_modules/@einfach-produktiv/invoicing": {
-      "version": "0.2.5",
-      "resolved": "git+https://git.mk360.de/Marco/einfach-produktiv-invoicing.git#bcdf8d2889bfc87fb2d5f12c8f80a311e491fd21",
+      "version": "0.2.6",
+      "resolved": "git+https://git.mk360.de/Marco/einfach-produktiv-invoicing.git#d6e83db5cf6343e65e2fa25f9ead49fce9a5a308",
       "dependencies": {
         "@e-invoice-eu/core": "^3.1.1"
       },