feat: add comprehensive demo mode with mock integrations (#5870)

packages/api/src/env.ts

@@ -1,12 +1,14 @@
 import { z } from "zod/v4";
 
-import { createEnv } from "@homarr/core/infrastructure/env";
+import { createBooleanSchema, createEnv } from "@homarr/core/infrastructure/env";
 
 export const env = createEnv({
   server: {
     KUBERNETES_SERVICE_ACCOUNT_NAME: z.string().optional(),
+    DEMO_MODE: createBooleanSchema(false),
   },
   runtimeEnv: {
     KUBERNETES_SERVICE_ACCOUNT_NAME: process.env.KUBERNETES_SERVICE_ACCOUNT_NAME,
+    DEMO_MODE: process.env.DEMO_MODE,
   },
 });