feat(api): add centralized API version config for frontend

- API_VERSION constant controls all frontend API paths
- API_PREFIX auto-derived: /api/v1
- API_URL combines base URL + prefix
- WS_URL for WebSocket connections (versioned)
- Helper functions: buildApiUrl(), buildWsUrl()
- LEGACY_API_URL for backward compatibility

Mirrors backend/config/api.py pattern.

Part of #55

Author: DevanshuNEU

frontend/src/config/api.ts

@@ -1,12 +1,59 @@
 /**
- * API Configuration
+ * API Configuration - Single Source of Truth for API Versioning
  * 
- * Centralizes API URL configuration for all frontend components.
+ * Change API_VERSION here to update all API calls across the frontend.
+ * Example: "v1" -> "v2" will change /api/v1/* to /api/v2/*
  */
 
-const API_URL = import.meta.env.VITE_API_URL || 'http://localhost:8000'
+// =============================================================================
+// BASE CONFIGURATION
+// =============================================================================
 
-// WebSocket URL - convert http(s) to ws(s)
-const WS_URL = API_URL.replace(/^http/, 'ws')
+const BASE_URL = import.meta.env.VITE_API_URL || 'http://localhost:8000'
 
-export { API_URL, WS_URL }
+// =============================================================================
+// API VERSION CONFIGURATION
+// =============================================================================
+
+export const API_VERSION = 'v1'
+
+// =============================================================================
+// DERIVED URLs (auto-calculated from version)
+// =============================================================================
+
+// API prefix: /api/v1
+export const API_PREFIX = `/api/${API_VERSION}`
+
+// Full API URL: http://localhost:8000/api/v1
+export const API_URL = `${BASE_URL}${API_PREFIX}`
+
+// WebSocket URL: ws://localhost:8000/api/v1
+const WS_BASE = BASE_URL.replace(/^http/, 'ws')
+export const WS_URL = `${WS_BASE}${API_PREFIX}`
+
+// Legacy URL (for backward compatibility if needed)
+export const LEGACY_API_URL = `${BASE_URL}/api`
+
+// =============================================================================
+// ENDPOINT HELPERS
+// =============================================================================
+
+/**
+ * Build a full API endpoint URL
+ * @param path - Endpoint path (e.g., '/repos', '/search')
+ * @returns Full URL (e.g., 'http://localhost:8000/api/v1/repos')
+ */
+export const buildApiUrl = (path: string): string => {
+  const cleanPath = path.startsWith('/') ? path : `/${path}`
+  return `${API_URL}${cleanPath}`
+}
+
+/**
+ * Build a WebSocket endpoint URL
+ * @param path - WebSocket path (e.g., '/ws/index/repo-123')
+ * @returns Full WS URL (e.g., 'ws://localhost:8000/api/v1/ws/index/repo-123')
+ */
+export const buildWsUrl = (path: string): string => {
+  const cleanPath = path.startsWith('/') ? path : `/${path}`
+  return `${WS_URL}${cleanPath}`
+}