fix(pdf-compress): fix broken multipart parsing + add body size limit

Extreme mode: replace fragile manual multipart boundary parsing (which
extracted only a fraction of large files, producing empty PDFs) with
standard req.formData(). Add GS output validation + stderr capture.

Stirling mode: parse formData first then build fresh FormData for
Stirling instead of raw body passthrough (which lost data on large
files). Add 5min timeout + original/compressed size headers.

next.config: add 250MB body size limit for server actions.

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

src/app/api/compress-pdf/route.ts

@@ -7,17 +7,42 @@ const STIRLING_PDF_API_KEY =
 
 export async function POST(req: NextRequest) {
   try {
-    // Stream body directly to Stirling — avoids FormData re-serialization
-    // failure on large files ("Failed to parse body as FormData")
+    // Parse incoming form data — get file + optimizeLevel
+    let formData: FormData;
+    try {
+      formData = await req.formData();
+    } catch (parseErr) {
+      const msg =
+        parseErr instanceof Error ? parseErr.message : "Parse error";
+      return NextResponse.json(
+        { error: `Nu s-a putut citi formularul: ${msg}` },
+        { status: 400 },
+      );
+    }
+
+    const fileField = formData.get("fileInput");
+    if (!fileField || !(fileField instanceof Blob)) {
+      return NextResponse.json(
+        { error: "Lipsește fișierul PDF." },
+        { status: 400 },
+      );
+    }
+
+    const optimizeLevel = formData.get("optimizeLevel") ?? "3";
+    const originalSize = fileField.size;
+
+    // Build fresh FormData for Stirling
+    const stirlingForm = new FormData();
+    stirlingForm.append("fileInput", fileField, "input.pdf");
+    stirlingForm.append("optimizeLevel", String(optimizeLevel));
+
     const res = await fetch(`${STIRLING_PDF_URL}/api/v1/misc/compress-pdf`, {
       method: "POST",
       headers: {
         "X-API-KEY": STIRLING_PDF_API_KEY,
-        "Content-Type": req.headers.get("content-type") || "",
       },
-      body: req.body,
-      // @ts-expect-error duplex required for streaming request bodies in Node
-      duplex: "half",
+      body: stirlingForm,
+      signal: AbortSignal.timeout(300_000), // 5 min for large files
     });
 
     if (!res.ok) {
@@ -36,6 +61,8 @@ export async function POST(req: NextRequest) {
       headers: {
         "Content-Type": "application/pdf",
         "Content-Disposition": 'attachment; filename="compressed.pdf"',
+        "X-Original-Size": String(originalSize),
+        "X-Compressed-Size": String(buffer.length),
       },
     });
   } catch (err) {