fix: percent-encode X-File-Results header to support non-ASCII filenames

The X-File-Results header contained raw JSON with non-ASCII characters
from filenames (Chinese, Japanese, etc.), violating RFC 7230. Node.js
threw ERR_INVALID_CHAR on writeHead(). Fixed by wrapping the JSON in
encodeURIComponent() on the backend and decodeURIComponent() on the
frontend, ensuring only ASCII goes into the header while preserving
the original filenames after decoding.

Closes #133

tests/integration/pipeline-edge-cases.test.ts

@@ -426,6 +426,33 @@ describe("Pipeline batch execution", () => {
     expect(res.headers["x-file-results"]).toBeDefined();
   });
 
+  it("handles non-ASCII filenames without ERR_INVALID_CHAR (#133)", async () => {
+    const { body, contentType } = createMultipartPayload([
+      { name: "file", filename: "图片.png", contentType: "image/png", content: PNG_200x150 },
+      { name: "file", filename: "写真テスト.png", contentType: "image/png", content: PNG_200x150 },
+      {
+        name: "pipeline",
+        content: JSON.stringify({
+          steps: [{ toolId: "resize", settings: { width: 50 } }],
+        }),
+      },
+    ]);
+
+    const res = await app.inject({
+      method: "POST",
+      url: "/api/v1/pipeline/batch",
+      headers: { "content-type": contentType, authorization: `Bearer ${adminToken}` },
+      body,
+    });
+
+    expect(res.statusCode).toBe(200);
+    const raw = res.headers["x-file-results"] as string;
+    expect(raw).not.toMatch(/[-￿]/);
+    const fileResults = JSON.parse(decodeURIComponent(raw));
+    expect(fileResults["0"]).toContain("图片");
+    expect(fileResults["1"]).toContain("写真テスト");
+  });
+
   it("rejects pipeline batch with no files", async () => {
     const { body, contentType } = createMultipartPayload([
       {