feat(config): add server config + can disable message-bus

- server now provide it's config via /api/config (possibility to feature flag)
- client use /api/config to enable / disable some features
- capability to disable the message bus, somme OPS may not want this feature and
  consume persistent connections from server (websocket):
  OXICLOUD_MESSAGEBUS_ENABLE (true by default)

example.env

@@ -1112,7 +1112,28 @@ OXICLOUD_WOPI_ENABLED=false
 #   * nginx `proxy_read_timeout` default 60s  → ping ≤ 30s
 #   * Cloudflare hard limit 100s              → ping ≤ 45s
 #   * Traefik with idleTimeout bumped to 3600s → 30s is safely under
-#OXICLOUD_RT_WS_KEEPALIVE_SECONDS=30
+#OXICLOUD_MESSAGEBUS_KEEPALIVE_SECONDS=30
+
+# Message bus master switch. When `false`, /api/rt/ws and
+# POST /api/rt/ticket are NOT registered at boot — Axum returns 404
+# for both, keeping monitoring dashboards free of 5xx noise. Clients
+# discover this via GET /api/config.features.message_bus and skip WS
+# setup entirely. Publish sites in the services stay unchanged (bus
+# still runs internally; publishes to no subscribers are cheap no-ops).
+#
+# Why an operator might turn this off: each logged-in browser holds a
+# persistent WebSocket connection while a folder view is open. Total
+# sustained sessions on the server = users × open tabs, each consuming
+# an fd, a few KB of tokio task state, and whatever tuple your L4/L7
+# load balancer keeps for the flow. On tightly-provisioned VPS
+# deployments (low fd ulimit, tight memory), behind WebSocket-hostile
+# reverse proxies that can't be reconfigured, or during an operational
+# triage where you want to shed WS load fast, set this to false — the
+# SPA falls back to its pre-message-bus behavior transparently
+# (updates land on the next nav / refresh instead of live).
+#
+# Default: true.
+#OXICLOUD_MESSAGEBUS_ENABLE=true
 
 # -----------------------------------------------------------------------------
 # MEMORY ALLOCATOR TUNING (IMPORTANT FOR RAM USAGE)