feat: adds PDF import with conversion to JSON 1.0

- Accept only PDF and JSON files in import modal and API
- Convert PDF statements to JSON 1.0 via LLM (OpenAI-compatible)
- Use multipart/form-data for file upload (multer, 15 MB limit)
- Add LLM_API_KEY and LLM_API_BASE_URL for configurable LLM endpoint
- Update ImportModal to validate type and send FormData
- Add postFormData to API client for file upload

backend/src/routes/import.ts

@@ -1,13 +1,81 @@
 import { Router } from 'express';
+import multer from 'multer';
 import { asyncHandler } from '../utils';
 import { importStatement, isValidationError } from '../services/import';
+import {
+  convertPdfToStatement,
+  isPdfConversionError,
+} from '../services/pdfToStatement';
+
+const upload = multer({
+  storage: multer.memoryStorage(),
+  limits: { fileSize: 15 * 1024 * 1024 },
+});
+
+function isPdfFile(file: { mimetype: string; originalname: string }): boolean {
+  const name = file.originalname.toLowerCase();
+  return (
+    file.mimetype === 'application/pdf' ||
+    name.endsWith('.pdf')
+  );
+}
+
+function isJsonFile(file: { mimetype: string; originalname: string }): boolean {
+  const name = file.originalname.toLowerCase();
+  return (
+    file.mimetype === 'application/json' ||
+    name.endsWith('.json')
+  );
+}
 
 const router = Router();
 
 router.post(
   '/statement',
+  upload.single('file'),
   asyncHandler(async (req, res) => {
-    const result = await importStatement(req.body);
+    const file = req.file;
+    if (!file) {
+      res.status(400).json({
+        error: 'BAD_REQUEST',
+        message: 'Файл не загружен',
+      });
+      return;
+    }
+
+    if (!isPdfFile(file) && !isJsonFile(file)) {
+      res.status(400).json({
+        error: 'BAD_REQUEST',
+        message: 'Допустимы только файлы PDF или JSON',
+      });
+      return;
+    }
+
+    let body: unknown;
+
+    if (isPdfFile(file)) {
+      const converted = await convertPdfToStatement(file.buffer);
+      if (isPdfConversionError(converted)) {
+        res.status(converted.status).json({
+          error: converted.error,
+          message: converted.message,
+        });
+        return;
+      }
+      body = converted;
+    } else {
+      try {
+        body = JSON.parse(file.buffer.toString('utf-8'));
+      } catch {
+        res.status(400).json({
+          error: 'BAD_REQUEST',
+          message: 'Некорректный JSON-файл',
+        });
+        return;
+      }
+    }
+
+    const result = await importStatement(body);
     if (isValidationError(result)) {
       res.status((result as { status: number }).status).json({
         error: (result as { error: string }).error,