feat(backend): 无界列表端点加分页——projects/templates 支持 limit/offset

GET /projects 与 GET /templates 原一次返回全部 owner 行，行数随数据线性增长。
新增可复用分页依赖 ww_api.pagination.get_page（limit∈[1,200] 默认 50、offset≥0，
越界 → 422），两端点接入，Repository.list_for_owner 加 keyword-only limit/offset
把 LIMIT/OFFSET 下推 DB。向后兼容：不传参返回第一页。补 projects 分页 + 边界 422 测试。

apps/api/tests/fakes_projects.py

@@ -63,8 +63,13 @@ class FakeProjectRepo:
         self.rows[pid] = (owner_id, view)
         return view
 
-    async def list_for_owner(self, owner_id: uuid.UUID) -> list[ProjectView]:
-        return [v for (o, v) in self.rows.values() if o == owner_id]
+    async def list_for_owner(
+        self, owner_id: uuid.UUID, *, limit: int | None = None, offset: int = 0
+    ) -> list[ProjectView]:
+        views = [v for (o, v) in self.rows.values() if o == owner_id]
+        if limit is None:
+            return views
+        return views[offset : offset + limit]
 
     async def get(self, owner_id: uuid.UUID, project_id: uuid.UUID) -> ProjectView | None:
         entry = self.rows.get(project_id)

apps/api/tests/test_projects.py

@@ -222,6 +222,33 @@ async def test_list_projects() -> None:
     assert all(p["pending_review_count"] == 0 for p in projects)
 
 
+@pytest.mark.asyncio
+async def test_list_projects_paginates_with_limit_and_offset() -> None:
+    client, _, _, _ = _make_client()
+    async with client:
+        for t in ("甲", "乙", "丙"):
+            await client.post("/projects", json={"title": t})
+        page1 = await client.get("/projects?limit=2")
+        page2 = await client.get("/projects?limit=2&offset=2")
+    assert page1.status_code == 200
+    assert [p["title"] for p in page1.json()["projects"]] == ["甲", "乙"]
+    assert page2.status_code == 200
+    assert [p["title"] for p in page2.json()["projects"]] == ["丙"]
+
+
+@pytest.mark.asyncio
+async def test_list_projects_rejects_out_of_range_pagination() -> None:
+    client, _, _, _ = _make_client()
+    async with client:
+        too_small = await client.get("/projects?limit=0")
+        too_large = await client.get("/projects?limit=201")
+        neg_offset = await client.get("/projects?offset=-1")
+    # 边界越界 → FastAPI 422（limit∈[1,200]、offset≥0）。
+    assert too_small.status_code == 422
+    assert too_large.status_code == 422
+    assert neg_offset.status_code == 422
+
+
 @pytest.mark.asyncio
 async def test_get_project_detail() -> None:
     client, _, _, _ = _make_client()

apps/api/tests/test_templates.py

@@ -33,8 +33,13 @@ class _FakeTemplateRepo:
         self.rows[view.id] = view
         return view
 
-    async def list_for_owner(self, owner_id: uuid.UUID) -> list[TemplateView]:
-        return list(self.rows.values())
+    async def list_for_owner(
+        self, owner_id: uuid.UUID, *, limit: int | None = None, offset: int = 0
+    ) -> list[TemplateView]:
+        views = list(self.rows.values())
+        if limit is None:
+            return views
+        return views[offset : offset + limit]
 
     async def delete(self, owner_id: uuid.UUID, template_id: uuid.UUID) -> bool:
         if template_id in self.rows: