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/embedder.py

@@ -5,8 +5,6 @@ from __future__ import annotations
 import logging
 from pathlib import Path
 
-import httpx
-from sqlalchemy import select
 from sqlalchemy.orm import Session, joinedload
 
 from app.config import settings
@@ -14,66 +12,82 @@ from app.models import Paper
 
 logger = logging.getLogger(__name__)
 
-# ── 单例客户端和 collection ─────────────────────────────────────────────
-_client = None
-_collection = None
+
+# ── ChromaDB 管理器（替代全局可变状态）──────────────────────────────────
 
 
-def _chroma_dir() -> Path:
-    return Path(settings.CHROMA_DIR)
+class ChromaManager:
+    """封装 ChromaDB 客户端和 collection 的生命周期。"""
+
+    def __init__(self) -> None:
+        self._client = None
+        self._collection = None
+
+    def init(self) -> None:
+        """CHROMA_ENABLED=true 时初始化 ChromaDB 持久客户端和 collection。"""
+        if not settings.CHROMA_ENABLED:
+            logger.debug("ChromaDB disabled, skip init")
+            return
+
+        if self._client is not None:
+            return
+
+        try:
+            import chromadb
+
+            chroma_path = Path(settings.CHROMA_DIR)
+            chroma_path.mkdir(parents=True, exist_ok=True)
+
+            self._client = chromadb.PersistentClient(path=str(chroma_path))
+            self._collection = self._get_or_create_collection()
+            logger.info("ChromaDB initialized at %s", chroma_path)
+        except Exception:
+            logger.exception("Failed to initialize ChromaDB")
+            self._client = None
+            self._collection = None
+
+    def _get_or_create_collection(self):
+        """获取或创建 papers_embeddings collection。"""
+        try:
+            col = self._client.get_collection("papers_embeddings")
+            logger.info("ChromaDB collection 'papers_embeddings' loaded, count=%d", col.count())
+            return col
+        except Exception:
+            pass
+
+        col = self._client.create_collection(
+            name="papers_embeddings",
+            metadata={"hnsw:space": "cosine"},
+        )
+        logger.info("ChromaDB collection 'papers_embeddings' created")
+        return col
+
+    def get_collection(self):
+        """返回当前 collection，未初始化则自动初始化。"""
+        if not settings.CHROMA_ENABLED:
+            return None
+        if self._collection is None:
+            self.init()
+        return self._collection
+
+    def reset(self) -> None:
+        """重置状态（供测试使用）。"""
+        self._client = None
+        self._collection = None
+
+
+# 模块级单例
+_chroma = ChromaManager()
 
 
 def init_chroma() -> None:
-    """CHROMA_ENABLED=true 时初始化 ChromaDB 持久客户端和 collection。"""
-    global _client, _collection
-    if not settings.CHROMA_ENABLED:
-        logger.debug("ChromaDB disabled, skip init")
-        return
-
-    if _client is not None:
-        return
-
-    try:
-        import chromadb
-
-        chroma_path = _chroma_dir()
-        chroma_path.mkdir(parents=True, exist_ok=True)
-
-        _client = chromadb.PersistentClient(path=str(chroma_path))
-        _collection = _get_or_create_collection()
-        logger.info("ChromaDB initialized at %s", chroma_path)
-    except Exception:
-        logger.exception("Failed to initialize ChromaDB")
-        _client = None
-        _collection = None
-
-
-def _get_or_create_collection():
-    """获取或创建 papers_embeddings collection，维度不匹配时记录日志并跳过。"""
-    import chromadb
-
-    try:
-        col = _client.get_collection("papers_embeddings")
-        logger.info("ChromaDB collection 'papers_embeddings' loaded, count=%d", col.count())
-        return col
-    except Exception:
-        pass
-
-    col = _client.create_collection(
-        name="papers_embeddings",
-        metadata={"hnsw:space": "cosine"},
-    )
-    logger.info("ChromaDB collection 'papers_embeddings' created")
-    return col
+    """初始化 ChromaDB（供 lifespan 调用）。"""
+    _chroma.init()
 
 
 def get_collection():
     """返回当前 collection，未初始化则返回 None。"""
-    if not settings.CHROMA_ENABLED:
-        return None
-    if _collection is None:
-        init_chroma()
-    return _collection
+    return _chroma.get_collection()
 
 
 # ── Embedding API 调用 ──────────────────────────────────────────────────
@@ -90,6 +104,8 @@ def _get_embedding(text: str) -> list[float] | None:
         logger.warning("EMBED_API_BASE or EMBED_MODEL not configured, skip embedding")
         return None
 
+    from app.utils import make_http_client
+
     url = f"{settings.EMBED_API_BASE.rstrip('/')}/v1/embeddings"
     headers = {"Content-Type": "application/json"}
     if settings.EMBED_API_KEY:
@@ -101,7 +117,7 @@ def _get_embedding(text: str) -> list[float] | None:
     }
 
     try:
-        with httpx.Client(timeout=settings.HTTP_TIMEOUT_SECONDS) as client:
+        with make_http_client(sync=True) as client:
             resp = client.post(url, json=payload, headers=headers)
             resp.raise_for_status()
             data = resp.json()