refactor: Phase 3 拆分 generate 流水线并补全测试

提取 collect/formatters/themes 等 pipeline 模块，新增 wecom 分条、RSS、delta、Agent 工作流测试。

Co-authored-by: Cursor <cursoragent@cursor.com>

daily/pipeline/snapshot.py

@@ -0,0 +1,36 @@
+"""Skills 快照读写。"""
+
+from __future__ import annotations
+
+import json
+from typing import Any
+
+from daily.config import CACHE_DIR, SNAPSHOT_FILE
+
+
+def skill_id(item: dict[str, Any]) -> str:
+    return str(item.get("id") or f"{item.get('source')}/{item.get('title')}")
+
+
+def load_snapshot() -> set[str]:
+    if not SNAPSHOT_FILE.exists():
+        return set()
+    try:
+        data = json.loads(SNAPSHOT_FILE.read_text(encoding="utf-8"))
+        return set(str(x) for x in (data.get("skill_ids") or []))
+    except (OSError, json.JSONDecodeError):
+        return set()
+
+
+def save_snapshot(feed: dict[str, Any], date_str: str) -> None:
+    CACHE_DIR.mkdir(parents=True, exist_ok=True)
+    ids: list[str] = []
+    for board in ("topTrending", "topHot"):
+        for item in feed.get(board, [])[:20]:
+            sid = skill_id(item)
+            if sid not in ids:
+                ids.append(sid)
+    SNAPSHOT_FILE.write_text(
+        json.dumps({"date": date_str, "skill_ids": ids}, ensure_ascii=False, indent=2),
+        encoding="utf-8",
+    )