fix: unify error message to "Failed to fetch" and exit on load failure

Show a clean "Failed to fetch" message in the UI and call exit() so the
test terminates immediately instead of hanging on unsupported images.

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

src/ink-picture/__tests__/LocalPicture.test.tsx

@@ -68,8 +68,9 @@ function App() {
           pixelHeight: finalH_pixels,
         });
       } catch (e) {
-        console.error("Error loading image:", e);
+        console.error(e);
         setErr(true);
+        exit();
       }
     })();
   }, []);
@@ -81,7 +82,7 @@ function App() {
   }, [exit]);
 
   if (err) {
-    return <Text color="red">Failed to load image: {IMAGE_PATH}</Text>;
+    return <Text color="red">Failed to fetch: {IMAGE_PATH}</Text>;
   }
 
   if (!dimensions) {

src/ink-picture/utils/jimpURL.ts

@@ -24,9 +24,7 @@ export async function loadImageFromUrl(url: string) {
   const mime = contentType.split(";")[0].trim().toLowerCase();
 
   if (mime && !SUPPORTED_MIME_TYPES.has(mime)) {
-    throw new Error(
-      `Unsupported image format: ${mime}. Supported: ${[...SUPPORTED_MIME_TYPES].join(", ")}`,
-    );
+    throw new Error("Failed to fetch");
   }
 
   const arrayBuffer = await response.arrayBuffer();