Add SABnzbd for Usenet NZB search and download

Wire Newshosting/Tweaknews via secrets-driven configure script, NZBgeek
through Prowlarr, and /data/usenet paths for hardlinks with the Arrs.

secrets/.env.example

@@ -0,0 +1,27 @@
+# Copy to secrets/.env and fill in. NEVER commit secrets/.env
+# Used by scripts/configure-usenet.sh and as a personal password vault.
+
+# --- NZBgeek (indexer — wire in Prowlarr) ---
+NZBGEEK_USERNAME=
+NZBGEEK_EMAIL=
+# API key from nzbgeek.info account (not the base URL)
+NZBGEEK_API_KEY=
+# Optional base URL (default https://api.nzbgeek.info/)
+NZBGEEK_URL=https://api.nzbgeek.info/
+
+# --- Newshosting (Usenet provider — SABnzbd server) ---
+NEWSHOSTING_HOST=news.newshosting.com
+NEWSHOSTING_PORT=563
+NEWSHOSTING_SSL=1
+NEWSHOSTING_USER=
+NEWSHOSTING_PASS=
+# Connections: start ~20 (plan-dependent)
+NEWSHOSTING_CONNECTIONS=20
+
+# --- Tweaknews (Usenet provider / fill-in block) ---
+TWEAKNEWS_HOST=news.tweaknews.eu
+TWEAKNEWS_PORT=563
+TWEAKNEWS_SSL=1
+TWEAKNEWS_USER=
+TWEAKNEWS_PASS=
+TWEAKNEWS_CONNECTIONS=10