Fix LAN API access and dev proxy routing

frontend/src/lib/api.test.ts

@@ -97,11 +97,11 @@ async function runApiTests(): Promise<void> {
     assert(await thumbnail.text() === 'preview-bytes', 'Thumbnail blob bytes mismatch');
     assert(await preview.text() === 'preview-bytes', 'Preview blob bytes mismatch');
     assert(
-      requestUrls[0] === 'http://localhost:8000/api/v1/documents/doc-1/thumbnail',
+      requestUrls[0] === '/api/v1/documents/doc-1/thumbnail',
       `Unexpected thumbnail URL ${requestUrls[0]}`,
     );
     assert(
-      requestUrls[1] === 'http://localhost:8000/api/v1/documents/doc-1/preview',
+      requestUrls[1] === '/api/v1/documents/doc-1/preview',
       `Unexpected preview URL ${requestUrls[1]}`,
     );
     assert(requestAuthHeaders[0] === null, `Expected no auth header for thumbnail request, got "${requestAuthHeaders[0]}"`);

frontend/src/lib/api.ts

@@ -14,7 +14,7 @@ import type {
 } from '../types';
 
 /**
- * Resolves backend base URL from environment with current-host HTTP fallback.
+ * Resolves backend base URL from environment with same-origin proxy fallback.
  */
 function resolveApiBase(): string {
   const envValue = import.meta.env?.VITE_API_BASE;
@@ -25,11 +25,7 @@ function resolveApiBase(): string {
     }
   }
 
-  if (typeof window !== 'undefined' && window.location?.hostname) {
-    return `http://${window.location.hostname}:8000/api/v1`;
-  }
-
-  return 'http://localhost:8000/api/v1';
+  return '/api/v1';
 }
 
 const API_BASE = resolveApiBase();