chore: prepare repo for public release — scrub internal infra, rewrite README

- Remove owner-specific / legacy deploy files (home/prod/server compose, deploy/).
  The home compose stays as a local untracked file for the maintainer's own deploy.
- Genericise infra-specific code comments (egress-proxy examples) to neutral wording.
- Replace the hardcoded contact email on the legal pages with the instance operator's
  configured admin email, served via the public /auth/config and shown with a neutral
  fallback — so each self-hosted instance shows its own contact.
- Rewrite README for the current app + a copy-paste self-hosting quick start (prebuilt
  image + first-run wizard) with a build-from-source alternative; tidy .env.example.

.env.example

@@ -48,15 +48,9 @@ SMTP_USER=
 SMTP_PASSWORD=
 SMTP_FROM=
 
-# --- Deployment role ---
-# DATABASE_URL is set automatically by docker-compose.yml / docker-compose.server.yml to the
-# bundled `db` service. Override it only for local dev against the central server DB, e.g.:
-#   DATABASE_URL=postgresql+psycopg://siftlode:<password>@your-db-host:5432/siftlode
-# Exactly one instance may run the background scheduler. The central server keeps it on; every
-# other instance (local dev, etc.) must set SCHEDULER_ENABLED=false. The compose files set this
-# for you (server=true via docker-compose.server.yml, local=false via docker-compose.localdev.yml).
+# --- Scheduler ---
+# The background scheduler (subscription sync, backfill, enrichment) runs inside the app.
+# DATABASE_URL is set for you by docker-compose to the bundled `db` service. If you ever run
+# more than one instance against the same database, keep SCHEDULER_ENABLED=true on exactly one
+# of them and false on the rest, to avoid double quota use and write races.
 SCHEDULER_ENABLED=true
-
-# On the central server, set this so backup.sh / restore.sh and plain `docker compose` commands
-# target the server stack automatically:
-#   COMPOSE_FILE=docker-compose.server.yml