feat(stacks): state-aware sidebar context menu and Open App action (#368)

* feat(stacks): state-aware sidebar context menu and Open App action

- Context menu now adapts to stack state: running stacks show
  Stop/Restart/Update, stopped stacks show Deploy only
- Added "Open App" shortcut to open a stack's web UI directly
  from the sidebar (visible when running with a published port)
- Backend bulk status endpoint enriched with mainPort detection
- Reduced manual image update check cooldown from 10 to 2 minutes
- Rate limit error message now derives from the configured constant

* fix(stacks): use const for bulkPorts (prefer-const lint)

backend/src/services/ImageUpdateService.ts

@@ -159,9 +159,13 @@ export class ImageUpdateService {
 
     private static readonly INTERVAL_MS = 6 * 60 * 60 * 1000;    // 6 hours
     private static readonly STARTUP_DELAY_MS = 2 * 60 * 1000;    // 2 min after boot
-    private static readonly MANUAL_COOLDOWN_MS = 10 * 60 * 1000; // 10 min between manual triggers
+    private static readonly MANUAL_COOLDOWN_MS = 2 * 60 * 1000;  // 2 min between manual triggers
     private static readonly INTER_IMAGE_DELAY_MS = 300;           // be polite to registries
 
+    public static get manualCooldownMinutes(): number {
+        return ImageUpdateService.MANUAL_COOLDOWN_MS / (60 * 1000);
+    }
+
     private constructor() { }
 
     public static getInstance(): ImageUpdateService {
@@ -186,7 +190,7 @@ export class ImageUpdateService {
 
     /**
      * Triggers a check immediately, unless one is already running or the
-     * 10-minute manual cooldown has not elapsed.
+     * manual cooldown (MANUAL_COOLDOWN_MS) has not elapsed.
      * Returns false if rate-limited, true if a check was started.
      */
     public triggerManualRefresh(): boolean {