Fix backend issues in desktop app (#4995)

# Description of Changes
Fixes two distinct but related issues in the backend of the desktop app:
- Correctly shows tools as unavaialable when the backend doesn't have
the dependencies or has disabled them etc. (same as web version - this
primarily didn't work on desktop because the app spawns before the
backend is running)
- Fixes infinite re-rendering issues caused by the app polling whether
the backend is healthy or not

frontend/src/core/contexts/AppConfigContext.tsx

@@ -42,6 +42,7 @@ export interface AppConfig {
   appVersion?: string;
   machineType?: string;
   activeSecurity?: boolean;
+  dependenciesReady?: boolean;
   error?: string;
 }
 

frontend/src/core/hooks/useBackendHealth.ts

@@ -4,8 +4,6 @@ export function useBackendHealth(): BackendHealthState {
   return {
     status: 'healthy',
     message: null,
-    isChecking: false,
-    lastChecked: Date.now(),
     error: null,
     isHealthy: true,
   };

frontend/src/core/types/backendHealth.ts

@@ -3,8 +3,6 @@ export type BackendStatus = 'stopped' | 'starting' | 'healthy' | 'unhealthy';
 export interface BackendHealthState {
   status: BackendStatus;
   message?: string | null;
-  lastChecked?: number;
-  isChecking: boolean;
   error: string | null;
   isHealthy: boolean;
 }