chore: migrate to v3, Doppler secrets, clean up legacy code

- Remove all pre-v3 code: scraper, ui-v2, backend v1, ios v1+v2, legacy CI workflows
- Flatten v3/ contents to repo root
- Add Doppler secrets management (project=libnovel, config=prd)
- Add justfile with doppler run wrappers for all docker compose commands
- Strip hardcoded env fallbacks from docker-compose.yml
- Add minimal README.md
- Clean up .gitignore

crowdsec/acquis.yaml

@@ -0,0 +1,12 @@
+# CrowdSec log acquisition — tells the CrowdSec agent which logs to parse.
+#
+# Caddy writes JSON access logs to /var/log/caddy/access.log (mounted from the
+# caddy_logs Docker volume).  CrowdSec reads the same volume at the same path.
+#
+# The `crowdsecurity/caddy` collection (installed via COLLECTIONS env var)
+# provides the parser that understands Caddy's JSON log format.
+
+filenames:
+  - /var/log/caddy/access.log
+labels:
+  type: caddy