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/widgets/AgentStatusWidget.tsx

@@ -5,6 +5,7 @@
 import { useState, useEffect } from "react";
 import { Bot, Activity, AlertCircle, CheckCircle, Clock } from "lucide-react";
 import type { WidgetProps } from "@mosaic/shared";
+import { ORCHESTRATOR_URL } from "@/lib/config";
 
 interface Agent {
   agentId: string;
@@ -28,10 +29,7 @@ export function AgentStatusWidget({ id: _id, config: _config }: WidgetProps): Re
       setError(null);
 
       try {
-        // Get orchestrator URL from environment or default to localhost
-        const orchestratorUrl = process.env.NEXT_PUBLIC_ORCHESTRATOR_URL ?? "http://localhost:8001";
-
-        const response = await fetch(`${orchestratorUrl}/agents`, {
+        const response = await fetch(`${ORCHESTRATOR_URL}/agents`, {
           headers: {
             "Content-Type": "application/json",
           },