Fix boot state sharing across Next.js module boundaries

Use globalThis for all in-memory stores (credentials, models, agents,
tasks) so the instrumentation hook and API route handlers share the
same data. Next.js bundles these as separate chunks with independent
module instances, causing boot-populated state to be invisible to
API routes.

apps/harness/src/lib/credentials.ts

@@ -13,8 +13,10 @@ export interface Credential {
   baseUrl?: string; // for self-hosted GitLab or custom endpoints
 }
 
-// In-memory store. Will be replaced with encrypted persistent storage.
-const credentials: Map<string, Credential> = new Map();
+// In-memory store shared via globalThis to survive Next.js module re-bundling.
+const g = globalThis as unknown as { __harnessCredentials?: Map<string, Credential> };
+g.__harnessCredentials ??= new Map();
+const credentials = g.__harnessCredentials;
 
 export function getAllCredentials(): Credential[] {
   return Array.from(credentials.values()).map(c => ({