fix: downgrade pdf-parse to 1.1.1 to eliminate native dependency

pdf-parse@2.4.5 depends on @napi-rs/canvas (native Skia binary compiled
with AVX instructions) which crashes with SIGILL on the Synology NAS CPU.
Version 1.1.1 is pure JavaScript and works on any architecture.

backend/package.json

@@ -18,7 +18,7 @@
     "express": "^5.2.1",
     "multer": "^2.1.1",
     "openai": "^6.27.0",
-    "pdf-parse": "^2.4.5",
+    "pdf-parse": "1.1.1",
     "pg": "^8.19.0",
     "uuid": "^13.0.0"
   },

backend/src/services/pdfToStatement.ts

@@ -63,17 +63,9 @@ export function isPdfConversionError(r: unknown): r is PdfConversionError {
   );
 }
 
-// Lazy-loaded to avoid crashing the app at startup — pdf-parse pulls in
-// @napi-rs/canvas (native Skia binary) which may fail on Alpine.
-let _PDFParse: typeof import('pdf-parse')['PDFParse'] | undefined;
-function loadPDFParse() {
-  if (!_PDFParse) {
-    // eslint-disable-next-line @typescript-eslint/no-require-imports
-    const mod = require('pdf-parse') as typeof import('pdf-parse');
-    _PDFParse = mod.PDFParse;
-  }
-  return _PDFParse;
-}
+// pdf-parse v1 default export: (buffer, options?) => Promise<{ text, numpages, info }>
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+const pdfParse: (buf: Buffer) => Promise<{ text: string }> = require('pdf-parse');
 
 export async function convertPdfToStatement(
   buffer: Buffer,
@@ -88,11 +80,8 @@ export async function convertPdfToStatement(
 
   let text: string;
   try {
-    const PDFParse = loadPDFParse();
-    const parser = new PDFParse({ data: buffer });
-    const result = await parser.getText();
+    const result = await pdfParse(buffer);
     text = result.text || '';
-    await parser.destroy();
   } catch (err) {
     console.error('PDF extraction error:', err);
     return {