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/pi_client.py

@@ -0,0 +1,160 @@
+"""pi CLI 调用与 JSON 提取 — 调用 pi 生成总结，从输出中提取结构化 JSON。"""
+
+from __future__ import annotations
+
+import asyncio
+import json
+import logging
+import re
+from pathlib import Path
+
+from app.config import settings
+
+logger = logging.getLogger(__name__)
+
+
+# ── 自定义异常 ──────────────────────────────────────────────────────────
+
+
+class PiTimeoutError(Exception):
+    pass
+
+
+class PiProcessError(Exception):
+    def __init__(self, returncode: int, stderr: str):
+        self.returncode = returncode
+        self.stderr = stderr
+        super().__init__(f"pi exited with code {returncode}: {stderr[:500]}")
+
+
+class JsonNotFoundError(Exception):
+    pass
+
+
+# ── meta.json ───────────────────────────────────────────────────────────
+
+
+def write_meta_json(paper) -> Path:
+    """写入 data/papers/{arxiv_id}/meta.json，返回路径。"""
+    from app.services.pdf_downloader import paper_dir
+
+    d = paper_dir(paper.arxiv_id)
+    d.mkdir(parents=True, exist_ok=True)
+    meta_path = d / "meta.json"
+
+    authors = [a.name for a in paper.authors]
+    tags = [t.tag for t in paper.tags]
+    meta = {
+        "arxiv_id": paper.arxiv_id,
+        "title_en": paper.title_en,
+        "abstract": paper.abstract or "",
+        "published_at": paper.published_at.isoformat() if paper.published_at else None,
+        "authors": authors,
+        "tags": tags,
+        "upvotes": paper.upvotes,
+    }
+    meta_path.write_text(json.dumps(meta, ensure_ascii=False, indent=2), encoding="utf-8")
+    return meta_path
+
+
+# ── pi CLI 调用 ────────────────────────────────────────────────────────
+
+
+async def call_pi(meta_path: Path, pdf_path: Path) -> str:
+    """调用 pi CLI 非交互模式，返回 stdout 文本。"""
+    arxiv_id = meta_path.parent.name
+    cmd = [
+        settings.PI_BIN,
+        "-p",
+        "--no-tools",
+        "--skill",
+        settings.SUMMARY_SKILL,
+        "请深度解读以下论文，并按指定 JSON schema 输出：",
+        f"@{meta_path}",
+        f"@{pdf_path}",
+    ]
+    logger.info("Calling pi for %s", arxiv_id)
+
+    proc = await asyncio.create_subprocess_exec(
+        *cmd,
+        stdout=asyncio.subprocess.PIPE,
+        stderr=asyncio.subprocess.PIPE,
+    )
+    try:
+        stdout, stderr = await asyncio.wait_for(
+            proc.communicate(),
+            timeout=settings.SUMMARY_TIMEOUT_SECONDS,
+        )
+    except asyncio.TimeoutError:
+        proc.kill()
+        await proc.wait()
+        raise PiTimeoutError(
+            f"pi timed out after {settings.SUMMARY_TIMEOUT_SECONDS}s"
+        )
+
+    if proc.returncode != 0:
+        raise PiProcessError(proc.returncode, stderr.decode("utf-8", errors="replace"))
+
+    return stdout.decode("utf-8", errors="replace")
+
+
+# ── JSON 提取 ──────────────────────────────────────────────────────────
+
+
+def extract_json(raw_output: str) -> dict:
+    """从 pi 输出中提取 JSON dict。三步策略：直接解析 → 代码块 → 最大花括号块。"""
+    # 策略 1：整体直接解析
+    stripped = raw_output.strip()
+    try:
+        result = json.loads(stripped)
+        if isinstance(result, dict) and "title_zh" in result:
+            return result
+    except json.JSONDecodeError:
+        pass
+
+    # 策略 2：提取 ```json ... ``` 代码块
+    fence_pattern = re.compile(r"```(?:json)?\s*\n(.*?)```", re.DOTALL)
+    for match in fence_pattern.finditer(raw_output):
+        try:
+            result = json.loads(match.group(1).strip())
+            if isinstance(result, dict) and "title_zh" in result:
+                return result
+        except json.JSONDecodeError:
+            continue
+
+    # 策略 3：匹配包含 title_zh 的最大 {...} 块
+    brace_pattern = re.compile(r"\{[^{}]*\"title_zh\"[^{}]*\}", re.DOTALL)
+    for match in brace_pattern.finditer(raw_output):
+        try:
+            return json.loads(match.group(0))
+        except json.JSONDecodeError:
+            continue
+
+    # 更宽松：找到最大的 { ... } 平衡块
+    best = None
+    best_len = 0
+    for i, ch in enumerate(raw_output):
+        if ch != "{":
+            continue
+        depth = 0
+        for j in range(i, len(raw_output)):
+            if raw_output[j] == "{":
+                depth += 1
+            elif raw_output[j] == "}":
+                depth -= 1
+            if depth == 0:
+                candidate = raw_output[i : j + 1]
+                if len(candidate) > best_len:
+                    try:
+                        parsed = json.loads(candidate)
+                        if isinstance(parsed, dict):
+                            best = parsed
+                            best_len = len(candidate)
+                    except json.JSONDecodeError:
+                        pass
+                break
+
+    if best is not None:
+        return best
+
+    raise JsonNotFoundError("no JSON object found in pi output")