fix: silent autosave, pending dedup, domain/cell_name pending, containers access

- Settings: remove Save buttons; autosave is silent (no toast on success, error only)
- Settings: loadAll() resets dirty flags to prevent stale autosave after discard
- app.py: fix domain/ip_range "actually changed" check — full identity is always
  sent on save so these were triggering pending on every keystroke regardless
- app.py: _dedup_changes handles port-change format "service field: old → new"
  (split on ':' not ' changed') so dns_port changed twice shows one entry
- app.py: domain + cell_name changes now go through pending restart banner;
  apply_domain/apply_cell_name write files immediately (reload=False) and set
  pending; Discard restores zone files + Caddyfile to pre-change state
- app.py: _set_pending_restart captures pre-change snapshot BEFORE config writes
  (was snapshotting after, making Discard a no-op)
- app.py: is_local_request reads /proc/net/route to allow the actual Docker
  bridge subnet (172.0.0.0/24) which is not RFC-1918; fixes Containers page 403
- container_manager: get_container_logs raises instead of swallowing exceptions
  so nonexistent container returns 500+error not 200+empty

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

webui/src/App.jsx

@@ -215,6 +215,7 @@ function AppCore() {
   const handleCancel = useCallback(async () => {
     await cellAPI.cancelPending();
     setPending({ needs_restart: false, changes: [] });
+    window.dispatchEvent(new CustomEvent('pic-config-discarded'));
   }, []);
 
   const navigation = [