feat: stream PDF import progress via SSE with global progress bar

Replace the synchronous PDF import with Server-Sent Events streaming
between the backend (LLM) and the browser. The user can now close the
import modal and continue working while the conversion runs — a fixed
progress bar in the Layout shows real-time stage and percentage.

backend/src/routes/import.ts

@@ -3,7 +3,7 @@ import multer from 'multer';
 import { asyncHandler } from '../utils';
 import { importStatement, isValidationError } from '../services/import';
 import {
-  convertPdfToStatement,
+  convertPdfToStatementStreaming,
   isPdfConversionError,
 } from '../services/pdfToStatement';
 
@@ -28,6 +28,10 @@ function isJsonFile(file: { mimetype: string; originalname: string }): boolean {
   );
 }
 
+function sseWrite(res: import('express').Response, data: Record<string, unknown>) {
+  res.write(`data: ${JSON.stringify(data)}\n\n`);
+}
+
 const router = Router();
 
 router.post(
@@ -51,28 +55,73 @@ router.post(
       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 {
+      res.setHeader('Content-Type', 'text/event-stream');
+      res.setHeader('Cache-Control', 'no-cache');
+      res.setHeader('Connection', 'keep-alive');
+      res.setHeader('X-Accel-Buffering', 'no');
+      res.flushHeaders();
+
       try {
-        body = JSON.parse(file.buffer.toString('utf-8'));
-      } catch {
-        res.status(400).json({
-          error: 'BAD_REQUEST',
-          message: 'Некорректный JSON-файл',
+        const converted = await convertPdfToStatementStreaming(
+          file.buffer,
+          (stage, progress, message) => {
+            sseWrite(res, { stage, progress, message });
+          },
+        );
+
+        if (isPdfConversionError(converted)) {
+          sseWrite(res, {
+            stage: 'error',
+            message: converted.message,
+          });
+          res.end();
+          return;
+        }
+
+        sseWrite(res, {
+          stage: 'import',
+          progress: 88,
+          message: 'Импорт в базу данных...',
+        });
+
+        const result = await importStatement(converted);
+        if (isValidationError(result)) {
+          sseWrite(res, {
+            stage: 'error',
+            message: (result as { message: string }).message,
+          });
+          res.end();
+          return;
+        }
+
+        sseWrite(res, {
+          stage: 'done',
+          progress: 100,
+          result,
+        });
+      } catch (err) {
+        console.error('SSE import error:', err);
+        sseWrite(res, {
+          stage: 'error',
+          message: 'Внутренняя ошибка сервера',
         });
-        return;
       }
+
+      res.end();
+      return;
+    }
+
+    // JSON files — synchronous response as before
+    let body: unknown;
+    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);