Add inline comments to core modules and code review notes

Added explanatory comments to server.py, freshrss_pipeline.py, pipeline.py,
freshrss.py, keyword_index.py, summary_loop.py, and filters/engine.py.
Also added CODE_REVIEW.md with prioritized improvement suggestions.

src/summary_mcp/workflows/freshrss_pipeline.py

@@ -1,5 +1,9 @@
 from __future__ import annotations
 
+# FreshRSS 全链路管道：拉取未读条目 -> 内容提取 -> LLM 摘要 -> 规则过滤 ->
+# 构建 OpenClaw delivery payload -> 写盘 -> 词元统计 -> 标记已读。
+# 生产入口：run_freshrss_pipeline()，由 MCP 工具 run_freshrss_openclaw_pipeline 调用。
+
 import json
 import os
 from datetime import UTC, date, datetime
@@ -46,6 +50,7 @@ def _load_json(path: Path) -> dict[str, Any]:
 
 
 def _load_required_env(name: str, value: str | None) -> str:
+    # 优先使用传入的 value，否则读取同名环境变量；两者均缺失时抛出 RuntimeError
     resolved = value or os.environ.get(name)
     if not resolved:
         raise RuntimeError(f"Missing required value: {name}.")
@@ -137,6 +142,7 @@ def run_freshrss_pipeline(
     item_reports: list[dict[str, Any]] = []
 
     for index, item in enumerate(items, start=1):
+        # 逐条处理：提取 -> 摘要 -> 过滤 -> 候选构建；任一步骤失败则记录状态后 continue
         item_key = f"item-{index:02d}"
         item_path = _maybe_path(debug_artifacts, resolved_output_dir / "items" / f"{item_key}.item.json")
         extracted_path = _maybe_path(debug_artifacts, resolved_output_dir / "extracted" / f"{item_key}.extracted.json")
@@ -256,6 +262,7 @@ def run_freshrss_pipeline(
 
     marked_count = 0
     if mark_read and delivered_item_ids:
+        # 仅标记成功投递（delivered）的 item；drop/review 的 item 保持未读状态
         client.mark_items_as_read(auth_token=auth_token, item_ids=delivered_item_ids)
         marked_count = len({item_id for item_id in delivered_item_ids if item_id})