Revert SSE streaming for PDF import, use synchronous flow

SSE streaming added unnecessary complexity and latency due to
buffering issues across Node.js event loop, Nginx proxy, and
Docker layers. Reverted to a simple synchronous request/response
for PDF conversion. Kept extractLlmErrorMessage for user-friendly
LLM errors, lazy-loaded pdf-parse, and extended Nginx timeout.

frontend/src/api/import.ts

@@ -11,74 +11,3 @@ export async function importStatement(
     formData,
   );
 }
-
-export interface SseProgressEvent {
-  stage: 'pdf' | 'llm' | 'import';
-  progress: number;
-  message: string;
-}
-
-export interface SseDoneEvent {
-  stage: 'done';
-  progress: 100;
-  result: ImportStatementResponse;
-}
-
-export interface SseErrorEvent {
-  stage: 'error';
-  message: string;
-}
-
-export type SseEvent = SseProgressEvent | SseDoneEvent | SseErrorEvent;
-
-export async function importStatementStream(
-  file: File,
-  onEvent: (event: SseEvent) => void,
-): Promise<void> {
-  const formData = new FormData();
-  formData.append('file', file);
-
-  const res = await fetch('/api/import/statement', {
-    method: 'POST',
-    body: formData,
-    credentials: 'include',
-  });
-
-  if (!res.ok) {
-    let msg = 'Ошибка импорта';
-    try {
-      const body = await res.json();
-      if (body.message) msg = body.message;
-    } catch { /* use default */ }
-    onEvent({ stage: 'error', message: msg });
-    return;
-  }
-
-  const reader = res.body?.getReader();
-  if (!reader) {
-    onEvent({ stage: 'error', message: 'Streaming не поддерживается' });
-    return;
-  }
-
-  const decoder = new TextDecoder();
-  let buffer = '';
-
-  while (true) {
-    const { done, value } = await reader.read();
-    if (done) break;
-
-    buffer += decoder.decode(value, { stream: true });
-
-    const lines = buffer.split('\n');
-    buffer = lines.pop() ?? '';
-
-    for (const line of lines) {
-      const trimmed = line.trim();
-      if (!trimmed.startsWith('data: ')) continue;
-      try {
-        const parsed = JSON.parse(trimmed.slice(6)) as SseEvent;
-        onEvent(parsed);
-      } catch { /* skip malformed lines */ }
-    }
-  }
-}