Fix: Strip whitespace from S3_PUBLIC_BASE_URL before building CDN URLs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/app/routers/images.py

@@ -30,7 +30,7 @@ def _error(detail: str, code: str, status: int):
 def _image_to_dict(
     image: Image, *, cdn_base: str | None = None, duplicate: bool | None = None
 ) -> dict[str, Any]:
-    _base = cdn_base.rstrip("/") if cdn_base else None
+    _base = cdn_base.strip().rstrip("/") if cdn_base else None
     file_url = f"{_base}/{image.storage_key}" if _base else f"/api/v1/images/{image.id}/file"
     thumbnail_url = (
         (f"{_base}/{image.thumbnail_key}" if _base else f"/api/v1/images/{image.id}/thumbnail")