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>

.env.example

@@ -12,6 +12,13 @@ POLITRACK_READER_PASSWORD=change-me-too
 POLITRACK_USER_AGENT=PolitrackBot/0.1 (+https://example.org/about; contact: you@example.org)
 POLITRACK_MIN_REQUEST_INTERVAL=2.0
 
+# Shown on /impressum and /datenschutz. Required before the site goes public (§ 5 ECG, §§ 24, 25 MedienG).
+# POLITRACK_LEGAL_NAME=
+# POLITRACK_LEGAL_ADDRESS=
+# POLITRACK_LEGAL_EMAIL=
+# Defaults to POLITRACK_LEGAL_EMAIL.
+# POLITRACK_CORRECTIONS_EMAIL=
+
 # Legislative periods of the Austrian parliament to ingest in detail (JSON list).
 POLITRACK_PARLAMENT_PERIODS=["XXVII","XXVIII"]