fix(#338): Standardize API base URL and auth mechanism across components

- Create centralized config module (apps/web/src/lib/config.ts) exporting:
  - API_BASE_URL: Main API server URL from NEXT_PUBLIC_API_URL
  - ORCHESTRATOR_URL: Orchestrator service URL from NEXT_PUBLIC_ORCHESTRATOR_URL
  - Helper functions for building full URLs
- Update client.ts to import from central config
- Update LoginButton.tsx to use API_BASE_URL from config
- Update useWebSocket.ts to use API_BASE_URL from config
- Update AgentStatusWidget.tsx to use ORCHESTRATOR_URL from config
- Update TaskProgressWidget.tsx to use ORCHESTRATOR_URL from config
- Update useGraphData.ts to use API_BASE_URL from config
  - Fixed wrong default port (was 8000, now uses correct 3001)
- Add comprehensive tests for config module
- Update useWebSocket tests to properly mock config module

Refs #338

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/web/src/components/mindmap/hooks/useGraphData.ts

@@ -4,6 +4,7 @@
 import { useCallback, useEffect, useState } from "react";
 import { useSession } from "@/lib/auth-client";
 import { handleSessionExpired, isSessionExpiring } from "@/lib/api";
+import { API_BASE_URL } from "@/lib/config";
 
 // API Response types
 interface TagDto {
@@ -119,7 +120,7 @@ interface UseGraphDataResult {
   searchNodes: (query: string) => Promise<KnowledgeNode[]>;
 }
 
-const API_BASE = process.env.NEXT_PUBLIC_API_URL ?? "http://localhost:8000";
+const API_BASE = API_BASE_URL;
 
 /**
  * Sanitize labels for Mermaid diagrams to prevent XSS