fix(imgproxy): switch from base64 to plain URL format

Use plain/ source URL format instead of base64 encoding.
Base64 was causing 404 errors from imgproxy.
Plain format verified working via direct curl tests.

lib/imgproxy.ts

@@ -13,22 +13,6 @@ interface ImgproxyOptions {
   extension?: string;
 }
 
-/**
- * Encodes a string to Base64 (URL-safe)
- */
-function encodeBase64(str: string): string {
-  if (typeof Buffer !== 'undefined') {
-    return Buffer.from(str)
-      .toString('base64')
-      .replace(/\+/g, '-')
-      .replace(/\//g, '_')
-      .replace(/=+$/, '');
-  } else {
-    // Fallback for browser environment if Buffer is not available
-    return window.btoa(str).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
-  }
-}
-
 export function getImgproxyUrl(src: string, options: ImgproxyOptions = {}): string {
   // Use local proxy path which is rewritten in next.config.mjs
   const baseUrl = '/_img';
@@ -71,10 +55,10 @@ export function getImgproxyUrl(src: string, options: ImgproxyOptions = {}): stri
     `g:${gravity}`,
   ].join('/');
 
-  // Using /unsafe/ for now as we don't handle signatures yet
-  // Format: <base_url>/unsafe/<options>/<base64_url>
+  // Using /unsafe/ with plain/ source URL format
+  // plain/ format works reliably with imgproxy URL mapping
+  // Format: <base_url>/unsafe/<options>/plain/<source_url>[@<extension>]
   const suffix = extension ? `@${extension}` : '';
-  const encodedSrc = encodeBase64(absoluteSrc + suffix);
 
-  return `${baseUrl}/unsafe/${processingOptions}/${encodedSrc}`;
+  return `${baseUrl}/unsafe/${processingOptions}/plain/${absoluteSrc}${suffix}`;
 }