Prepare for going public: legal pages, corrections contact, portrait proxy

/impressum and /datenschutz read the operator's details from the environment
so they stay out of this repository, and show a visible notice until set.
Portraits go through an allowlisted /api/img so visitors' IPs stay with us.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docker-compose.yml

@@ -84,6 +84,11 @@ services:
     restart: unless-stopped
     environment:
       API_INTERNAL_URL: http://api:8000
+      POLITRACK_USER_AGENT: ${POLITRACK_USER_AGENT:-}
+      POLITRACK_LEGAL_NAME: ${POLITRACK_LEGAL_NAME:-}
+      POLITRACK_LEGAL_ADDRESS: ${POLITRACK_LEGAL_ADDRESS:-}
+      POLITRACK_LEGAL_EMAIL: ${POLITRACK_LEGAL_EMAIL:-}
+      POLITRACK_CORRECTIONS_EMAIL: ${POLITRACK_CORRECTIONS_EMAIL:-}
     ports:
       - "${WEB_PORT:-3000}:3000"
     depends_on: