fix: use 2.20.15 instead of 3.0.5, direct 2.13->3.0 migration is blocked

paperless-ngx v3 refuses to migrate from anything before v2.20.15
(paperless.E002). 2.20.15 already covers the API version range the
iOS app needs, so it fixes the phone upload issue without the v3
breaking changes.

k8s/apps/paperless/configmap.yaml

@@ -7,8 +7,6 @@ data:
   PAPERLESS_TIME_ZONE: "America/Los_Angeles"
   PAPERLESS_OCR_LANGUAGE: "eng"
   PAPERLESS_DBHOST: "paperless-db-rw"
-  # v3 requires this explicit - previously inferred from PAPERLESS_DBHOST
-  PAPERLESS_DBENGINE: "postgresql"
   PAPERLESS_DBNAME: "paperless"
   PAPERLESS_REDIS: "redis://paperless-redis:6379"
   # django-allauth generic OIDC provider. The client_id/secret/server_url

k8s/apps/paperless/deployment.yaml

@@ -35,7 +35,7 @@ spec:
         kubernetes.io/hostname: talos-cp-3
       containers:
         - name: paperless
-          image: ghcr.io/paperless-ngx/paperless-ngx:3.0.5
+          image: ghcr.io/paperless-ngx/paperless-ngx:2.20.15
           ports:
             - containerPort: 8000
           envFrom: