papra: add required AUTH_SECRET (app refuses to boot without it)

papra was NOT version-bumped by this campaign -- it crash-looped at its existing
26.6.1-rootless pin, so this is a PRE-EXISTING catalog defect: papra has never
been deployable from this template.

  Invalid configuration: In production, the auth secret must not be the default
  one. Please set a secure auth secret using the AUTH_SECRET environment
  variable.

Added as a generated hex:32 secret and marked data_key: true -- it signs
sessions, so regenerating it on restore would invalidate every login.

Campaign 7 catalog sweep.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Nn3VgQk9iwEGgyx6QJ2NvE

templates/papra/docker-compose.yml

@@ -14,6 +14,7 @@ services:
     environment:
       - TZ=Europe/Budapest
       - APP_BASE_URL=https://${SUBDOMAIN}.${DOMAIN}
+      - AUTH_SECRET=${AUTH_SECRET}
     volumes:
       - papra_data:/app/data
     networks: