refactor: rebrand compose, env and docs to BookmarkManager

.env.example

@@ -10,7 +10,7 @@ ALLOWED_ORIGINS=https://asuracomic.net,https://asurascans.com,https://demonicsca
 
 # --- Prod override (Traefik) only ---
 # Subdomain Traefik routes to this service (required by the prod override).
-# MANGA_API_HOST=manga-api.example.com
+# BOOKMARK_API_HOST=bookmark-api.example.com
 # Traefik's docker network name, if not "proxy".
 # PROXY_NETWORK=proxy
 # Traefik HTTPS entrypoint + cert resolver names, if yours differ from these.
@@ -18,7 +18,7 @@ ALLOWED_ORIGINS=https://asuracomic.net,https://asurascans.com,https://demonicsca
 # TRAEFIK_CERTRESOLVER=le
 
 # --- Web UI ---
-# Password for the browser UI at https://$MANGA_WEB_HOST. Leave unset to
+# Password for the browser UI at https://$BOOKMARK_WEB_HOST. Leave unset to
 # disable the web UI entirely (the routes are not registered at all).
 # Generate one: openssl rand -base64 18
 WEB_PASSWORD=
@@ -27,8 +27,8 @@ WEB_PASSWORD=
 # whether or not WEB_PASSWORD is set). Left commented on purpose: an example
 # value here would be a silent wrong-hostname fallback, and Traefik would
 # publish the UI router on a domain you do not own. The same container also
-# answers on MANGA_API_HOST for the userscript's API.
-# MANGA_WEB_HOST=manga.example.com
+# answers on BOOKMARK_API_HOST for the userscript's API.
+# BOOKMARK_WEB_HOST=bookmark.example.com
 
 # --- Latest-chapter poller ---
 # The backend re-checks each bookmarked series' newest published chapter on its