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.

frontend/src/context/ImportContext.tsx

@@ -0,0 +1,105 @@
+import {
+  createContext,
+  useContext,
+  useState,
+  useCallback,
+  useRef,
+  type ReactNode,
+} from 'react';
+import type { ImportStatementResponse } from '@family-budget/shared';
+import { importStatementStream, type SseEvent } from '../api/import';
+
+export interface ImportProgress {
+  active: boolean;
+  stage: string;
+  progress: number;
+  message: string;
+  result?: ImportStatementResponse;
+  error?: string;
+}
+
+interface ImportContextValue {
+  importState: ImportProgress;
+  startImport: (file: File) => void;
+  clearImport: () => void;
+}
+
+const INITIAL: ImportProgress = {
+  active: false,
+  stage: '',
+  progress: 0,
+  message: '',
+};
+
+const ImportContext = createContext<ImportContextValue | null>(null);
+
+export function ImportProvider({ children }: { children: ReactNode }) {
+  const [importState, setImportState] = useState<ImportProgress>(INITIAL);
+  const runningRef = useRef(false);
+
+  const startImport = useCallback((file: File) => {
+    if (runningRef.current) return;
+    runningRef.current = true;
+
+    setImportState({
+      active: true,
+      stage: 'pdf',
+      progress: 0,
+      message: 'Загрузка файла...',
+    });
+
+    importStatementStream(file, (event: SseEvent) => {
+      if (event.stage === 'done') {
+        setImportState({
+          active: false,
+          stage: 'done',
+          progress: 100,
+          message: 'Импорт завершён',
+          result: event.result,
+        });
+        runningRef.current = false;
+      } else if (event.stage === 'error') {
+        setImportState({
+          active: false,
+          stage: 'error',
+          progress: 0,
+          message: event.message,
+          error: event.message,
+        });
+        runningRef.current = false;
+      } else {
+        setImportState({
+          active: true,
+          stage: event.stage,
+          progress: event.progress,
+          message: event.message,
+        });
+      }
+    }).catch((err) => {
+      setImportState({
+        active: false,
+        stage: 'error',
+        progress: 0,
+        message: err instanceof Error ? err.message : 'Ошибка импорта',
+        error: err instanceof Error ? err.message : 'Ошибка импорта',
+      });
+      runningRef.current = false;
+    });
+  }, []);
+
+  const clearImport = useCallback(() => {
+    setImportState(INITIAL);
+  }, []);
+
+  return (
+    <ImportContext.Provider value={{ importState, startImport, clearImport }}>
+      {children}
+    </ImportContext.Provider>
+  );
+}
+
+export function useImport(): ImportContextValue {
+  const ctx = useContext(ImportContext);
+  if (!ctx) throw new Error('useImport must be used within ImportProvider');
+  return ctx;
+}