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/routes/trends.py

@@ -2,34 +2,27 @@
 
 from __future__ import annotations
 
-import logging
-from datetime import date, timedelta
-
 from fastapi import APIRouter, Depends, Request
-from fastapi.templating import Jinja2Templates
-from sqlalchemy import func, text
 from sqlalchemy.orm import Session
 
-from app.config import settings
 from app.database import get_db
-
-logger = logging.getLogger(__name__)
+from app.services.trends import get_trends_data
+from app.utils import templates, today_str
 
 router = APIRouter()
-templates = Jinja2Templates(directory="app/templates")
 
 
 @router.get("/trends")
 def trends_page(request: Request, db: Session = Depends(get_db)):
     """趋势看板页面。"""
-    stats = _get_trends_data(db)
+    stats = get_trends_data(db)
     return templates.TemplateResponse(
         request,
         "trends.html",
         {
             "page_title": "趋势看板",
             "stats": stats,
-            "today": _today_str(),
+            "today": today_str(),
         },
     )
 
@@ -37,84 +30,4 @@ def trends_page(request: Request, db: Session = Depends(get_db)):
 @router.get("/api/stats/trends")
 def trends_api(db: Session = Depends(get_db)):
     """趋势数据 JSON API。"""
-    return _get_trends_data(db)
-
-
-def _get_trends_data(db: Session) -> dict:
-    """从 DB 聚合趋势数据。"""
-    thirty_days_ago = (date.today() - timedelta(days=30)).isoformat()
-
-    # 1. 按日论文数量（近 30 天）
-    daily_rows = db.execute(text("""
-        SELECT paper_date, COUNT(*) as cnt
-        FROM papers
-        WHERE paper_date >= :start_date
-        GROUP BY paper_date
-        ORDER BY paper_date ASC
-    """), {"start_date": thirty_days_ago}).fetchall()
-    daily_counts = [
-        {"date": str(row[0]), "count": row[1]}
-        for row in daily_rows
-    ]
-
-    # 2. 热门标签 Top 20
-    tag_rows = db.execute(text("""
-        SELECT tag, COUNT(*) as cnt
-        FROM paper_tags
-        GROUP BY tag
-        ORDER BY cnt DESC
-        LIMIT 20
-    """)).fetchall()
-    top_tags = [
-        {"tag": row[0], "count": row[1]}
-        for row in tag_rows
-    ]
-
-    # 3. Upvotes 分布
-    upvote_rows = db.execute(text("""
-        SELECT
-            CASE
-                WHEN upvotes >= 100 THEN '100+'
-                WHEN upvotes >= 50 THEN '50-99'
-                WHEN upvotes >= 20 THEN '20-49'
-                WHEN upvotes >= 10 THEN '10-19'
-                WHEN upvotes >= 5 THEN '5-9'
-                ELSE '0-4'
-            END as bucket,
-            COUNT(*) as cnt
-        FROM papers
-        GROUP BY bucket
-        ORDER BY MIN(upvotes) DESC
-    """)).fetchall()
-    upvotes_dist = [
-        {"range": row[0], "count": row[1]}
-        for row in upvote_rows
-    ]
-
-    # 4. 总结完成率
-    summary_rows = db.execute(text("""
-        SELECT
-            COALESCE(ss.status, 'none') as status,
-            COUNT(*) as cnt
-        FROM papers p
-        LEFT JOIN summary_status ss ON ss.paper_id = p.id
-        GROUP BY status
-    """)).fetchall()
-    summary_completion = [
-        {"status": row[0], "count": row[1]}
-        for row in summary_rows
-    ]
-
-    return {
-        "daily_counts": daily_counts,
-        "top_tags": top_tags,
-        "upvotes_dist": upvotes_dist,
-        "summary_completion": summary_completion,
-    }
-
-
-def _today_str() -> str:
-    from datetime import datetime
-    from zoneinfo import ZoneInfo
-    tz = ZoneInfo(settings.APP_TIMEZONE)
-    return datetime.now(tz).strftime("%Y-%m-%d")
+    return get_trends_data(db)