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

frontend/src/components/ImportModal.tsx

@@ -22,23 +22,27 @@ export function ImportModal({ onClose, onDone }: Props) {
     const file = e.target.files?.[0];
     if (!file) return;
 
+    const name = file.name.toLowerCase();
+    const type = file.type;
+    const isPdf = type === 'application/pdf' || name.endsWith('.pdf');
+    const isJson = type === 'application/json' || name.endsWith('.json');
+
+    if (!isPdf && !isJson) {
+      setError('Допустимы только файлы PDF или JSON');
+      return;
+    }
+
     setLoading(true);
     setError('');
     setResult(null);
 
     try {
-      const text = await file.text();
-      const json = JSON.parse(text);
-      const resp = await importStatement(json);
+      const resp = await importStatement(file);
       setResult(resp);
     } catch (err: unknown) {
-      if (err instanceof SyntaxError) {
-        setError('Некорректный JSON-файл');
-      } else {
-        const msg =
-          err instanceof Error ? err.message : 'Ошибка импорта';
-        setError(msg);
-      }
+      const msg =
+        err instanceof Error ? err.message : 'Ошибка импорта';
+      setError(msg);
     } finally {
       setLoading(false);
     }
@@ -69,11 +73,11 @@ export function ImportModal({ onClose, onDone }: Props) {
 
           {!result && (
             <div className="import-upload">
-              <p>Выберите JSON-файл выписки (формат 1.0)</p>
+              <p>Выберите файл выписки (PDF или JSON, формат 1.0)</p>
               <input
                 ref={fileRef}
                 type="file"
-                accept=".json"
+                accept=".pdf,.json,application/pdf,application/json"
                 onChange={handleFileChange}
                 className="file-input"
               />