chore: add .gitignore, CrowdSec acquis config, update architecture docs

- .gitignore: exclude crowdsec/.crowdsec.env (bouncer API key), .env.local,
  and compiled Go binaries (backend/bin/, backend/healthcheck)
- crowdsec/acquis.yaml: log acquisition config for CrowdSec agent
- docs: update d2 and mermaid diagrams to reflect MinIO bucket renames
  (libnovel-chapters→chapters, libnovel-audio→audio, libnovel-browse→catalogue),
  remove /api/browse, update presigned URL paths

v3/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