ws: migrate push stream to data streaming

- daemon: send full snapshot on connect; versions/tick now carry the
  full state of one subsystem (subsystem + data); no legacy
  updated/subsystems payloads; refresh_state and POST /status/refresh
  broadcast per-subsystem versions with data
- client: modelSet() patches models in place; onMessage/topic refresh
  retired; 3s initial-load fallback via new POST /api/status/refresh
- schema: lib/schema.py TypedDicts + hoover/schema.js defaults +
  docs/state-model.md as single source of truth for state shapes
- system: poll at 1s, volatile metrics registered, dashboard uses a
  dedicated system model (status model removed)
- firewall: refuse to strip both https and ssh from the default zone
  (409, force override via UI confirm); set_zone_services persists
  services to the declarative config; collector exposes default_zone
- UI: pages migrate to flat state shapes; post-mutation modelFetch
  refreshes removed (WS delta covers it)
- tests: ws snapshot/delta/broadcast, refresh-state, schema types,
  model-set/js ws handler and reconnect fallback

docs/config.md

@@ -534,6 +534,10 @@ The `zones` object maps zone names (keys) to zone configurations. Each zone corr
 
 The `config_pending()` function compares the declarative config in `config/firewall/config.json` against the live firewalld state returned by the daemon (via `daemon.handlers.firewall.get_state()`). It returns a diff indicating which zones have pending changes for interfaces, services, target, masquerade, forward ports, and rich rules. Zones that exist live but not in config are reported as `unmanaged_zones`.
 
+Both `/api/firewall/zones/<name>/services` and `/api/firewall/config/apply` reconcile **remove-then-add** against the live zone, so anything opened outside the declarative config (e.g. directly via `firewall-cmd`) is reverted on the next apply. Service changes made through the API are persisted to `config.json` to prevent this drift.
+
+**Management-lockout guard.** The firewalld *default zone* is the catch-all for interfaces with no explicit assignment (typically the WAN), and it carries the management plane (nginx https) plus remote recovery (ssh). Changing the default zone's service set so that **neither `https` nor `ssh`** remains raises `409 Conflict` — from `POST /firewall/zones/<name>/services` and `POST /firewall/config/apply` — before any mutation runs. Send `"force": true` in the request body to override (the UI shows a confirm dialog with this effect on the Zones page). If the default zone cannot be determined, the guard fails closed.
+
 ## Networkd (IP Configuration)
 
 **File**: `config/network/config.json`