fix: Add redirect stage so matrix-invitation ends up at Element, not authentik dashboard

After the login stage, the flow had no destination, so it fell back to
authentik's own /if/user/ interface - which refuses type=external users
(the correct type for Matrix-only accounts), showing "Die Oberflaeche
kann nur von internen Nutzern geoeffnet werden". Added a static redirect
to https://axion1337.chat as the final stage.

apps/authentik/authentik-blueprints.yaml

@@ -78,3 +78,24 @@ data:
           order: 4
         attrs:
           stage: !Find [authentik_stages_user_login.userloginstage, [name, default-source-enrollment-login]]
+
+      # Without an explicit destination, the flow falls back to Authentik's own
+      # /if/user/ dashboard, which refuses type=external users ("Die Oberflaeche
+      # kann nur von internen Nutzern geoeffnet werden") - exactly the user type
+      # these Matrix-only accounts correctly have. Send them to Element instead.
+      - model: authentik_stages_redirect.redirectstage
+        state: present
+        identifiers:
+          name: matrix-invitation-redirect
+        id: matrix_invitation_redirect_stage
+        attrs:
+          mode: static
+          target_static: https://axion1337.chat
+
+      - model: authentik_flows.flowstagebinding
+        state: present
+        identifiers:
+          target: !KeyOf matrix_invitation_flow
+          order: 5
+        attrs:
+          stage: !KeyOf matrix_invitation_redirect_stage