refactor: restructure services and add image/pdf extraction utilities

- Add image_extractor, pdf_downloader, pi_client, trends services
- Add shared utils module
- Refactor summarizer, embedder, routes for cleaner separation
- Update tests to match new service structure

app/services/crawler.py

@@ -16,6 +16,7 @@ from app.models import (
     PaperTag,
     SummaryStatus,
 )
+from app.utils import make_http_client
 
 logger = logging.getLogger(__name__)
 
@@ -34,15 +35,7 @@ async def fetch_daily(target_date: str, top_n: int | None = None) -> list[dict]:
     url = f"{settings.HF_API_BASE}/daily_papers"
     params = {"date": target_date}
 
-    transport = None
-    if settings.http_proxy:
-        transport = httpx.AsyncHTTPTransport(proxy=settings.http_proxy)
-
-    async with httpx.AsyncClient(
-        timeout=settings.HTTP_TIMEOUT_SECONDS,
-        headers={"User-Agent": settings.HTTP_USER_AGENT},
-        transport=transport,
-    ) as client:
+    async with make_http_client() as client:
         for attempt in range(1, settings.HTTP_MAX_RETRIES + 1):
             try:
                 logger.info("Fetching HF Daily Papers: date=%s attempt=%d", target_date, attempt)