Alerts tab, Docker tab, nine new skins including HUD, a colour for every machine

Alerts: rules over sensors, watched fleet-wide from the hub; ntfy and webhook channels;
firing count on the rail. Docker: containers by stack with live use, start/stop/restart,
following logs, inspect, images/volumes/networks. Skins: HUD, Nord, Gruvbox, Catppuccin
(+Latte), Dracula, Tokyo Night, Solarized (+Light). Accents: per-machine colour.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

internal/store/store.go

@@ -21,6 +21,7 @@ type State struct {
 	Sessions  map[string]time.Time `json:"sessions"`            // token -> expiry
 	Dashboard json.RawMessage      `json:"dashboard,omitempty"` // UI layout prefs, opaque to the server
 	UI        json.RawMessage      `json:"ui,omitempty"`        // theme etc., opaque to the server
+	Alerts    json.RawMessage      `json:"alerts,omitempty"`    // rules, channels and recent events (internal/api/alerts.go)
 }
 
 type Store struct {