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>

tests/test_delta.py

@@ -0,0 +1,67 @@
+from __future__ import annotations
+
+import json
+
+import pytest
+
+
+def test_build_movement_context_detects_new_skill(isolated_output, monkeypatch):
+    import daily.config as config
+    import daily.delta as delta
+
+    monkeypatch.setattr(config, "OUTPUT_DIR", isolated_output)
+    monkeypatch.setattr(delta, "OUTPUT_DIR", isolated_output)
+
+    prev_path = isolated_output / "2026-07-02.data.json"
+    prev_path.write_text(
+        json.dumps(
+            {
+                "data": {
+                    "date": "2026-07-02",
+                    "movement_baseline": {
+                        "skills_trending": [{"id": "a/old", "title": "old"}],
+                        "skills_hot": [],
+                        "github_trending": [],
+                        "github_emerging": [],
+                        "github_topic": [],
+                    },
+                }
+            },
+            ensure_ascii=False,
+        ),
+        encoding="utf-8",
+    )
+
+    trending = [
+        {"id": "a/new", "title": "new-skill", "source": "a", "installs": 10, "link": "https://x", "description": ""},
+        {"id": "a/old", "title": "old", "source": "a", "installs": 9, "link": "https://y", "description": ""},
+    ]
+    movement = delta.build_movement_context(
+        date_str="2026-07-03",
+        trending=trending,
+        hot=[],
+        github_trending=[],
+        github_emerging=[],
+        github_topic=[],
+    )
+
+    assert movement["baseline_date"] == "2026-07-02"
+    assert len(movement["skills_trending_moves"]) == 1
+    assert movement["skills_trending_moves"][0]["id"] == "a/new"
+
+
+def test_find_previous_data_skips_missing_days(isolated_output, monkeypatch):
+    import daily.config as config
+    import daily.delta as delta
+
+    monkeypatch.setattr(config, "OUTPUT_DIR", isolated_output)
+    monkeypatch.setattr(delta, "OUTPUT_DIR", isolated_output)
+
+    (isolated_output / "2026-07-01.data.json").write_text(
+        json.dumps({"data": {"date": "2026-07-01", "skills_trending": []}}),
+        encoding="utf-8",
+    )
+
+    found = delta.find_previous_data("2026-07-03")
+    assert found is not None
+    assert found[0] == "2026-07-01"