Fix Docker deployment: Replace hardcoded localhost:3000 with environment-aware URLs

- Fixed API client to respect empty VITE_API_URL for same-origin requests
- Fixed video URL construction in videoPlaylist.ts
- Fixed video URL construction in VideoUpload.tsx
- All three files now use explicit undefined check instead of || operator
- Enables proper same-origin requests via nginx proxy in Docker

Co-Authored-By: Auggie

packages/frontend/src/components/admin/VideoUpload.tsx

@@ -24,7 +24,7 @@ export function VideoUpload({ term, onSuccess, onCancel }: VideoUploadProps) {
   const existingVideos = term.media?.filter(m => m.kind === MediaKind.VIDEO) || [];
 
   // Construct full video URL
-  const API_URL = import.meta.env.VITE_API_URL || 'http://localhost:3000';
+  const API_URL = import.meta.env.VITE_API_URL !== undefined ? import.meta.env.VITE_API_URL : 'http://localhost:3000';
   const getVideoUrl = (url: string) => url.startsWith('http') ? url : `${API_URL}${url}`;
 
   const validateFile = (file: File): boolean => {

packages/frontend/src/lib/api.ts

@@ -1,6 +1,6 @@
 import axios from 'axios';
 
-const API_URL = import.meta.env.VITE_API_URL || 'http://localhost:3000';
+const API_URL = import.meta.env.VITE_API_URL !== undefined ? import.meta.env.VITE_API_URL : 'http://localhost:3000';
 
 export const api = axios.create({
   baseURL: API_URL,

packages/frontend/src/lib/videoPlaylist.ts

@@ -39,7 +39,7 @@ export function getVideoUrl(relativeUrl: string | null): string | null {
   if (relativeUrl.startsWith('http')) return relativeUrl;
 
   // Construct full URL using backend base URL
-  const baseUrl = import.meta.env.VITE_API_URL || 'http://localhost:3000';
+  const baseUrl = import.meta.env.VITE_API_URL !== undefined ? import.meta.env.VITE_API_URL : 'http://localhost:3000';
   return `${baseUrl}${relativeUrl}`;
 }