fix(scripts): workspace-wide parent_path listing + private visibility on reads

1. 同 workspace 互相可见(排除 private):
   - list_scripts / count_scripts 已 workspace-wide + visibility 过滤,但
     单条读取(get/content/latest-version/versions)不校验 visibility,非
     owner 猜 id 即可读他人 private 脚本。新增 script_can_view(与 data
     resources 的 can_view 对称)并在 get_script_row / latest_version 强制,
     private 对非 owner 返回 404。

2. parent_path 为空默认拉根路径文件:
   - 物理存储为 workspace/{user_id}/...,根 prefix 原来是 workspace/ +
     NOT LIKE workspace/%/%,所有文件都在两层被整体排除,list_scripts("")
     恒空。改为 workspace/%/,配合 LIKE workspace/%/% AND NOT LIKE
     workspace/%/%/% 返回各 owner 根级文件。

3. 非空 parent_path 跨 owner 查询:
   - 原来 workspace/foo/ 永远匹配不到 workspace/{uid}/foo/...,子目录
     懒加载返回空,其他用户目录点击无内容。改为 workspace/%/foo/(owner
     段通配,与 list_resources 一致),_ / % 仍按字面转义。

测试:更新前缀契约断言,新增 SQLite 行为测试(跨 owner 根/子目录、转义)
与 script_can_view / get_script 权限测试,133 passed。

backend/tests/test_count_scripts.py

@@ -68,10 +68,11 @@ async def test_count_scripts_returns_scalar_int() -> None:
     # JOIN to StorageObjects so orphaned scripts (no joinable row) are
     # excluded — matches list_scripts INNER JOIN behaviour.
     assert "inner join storage_objects" in sql
-    # Scope: workspace_id + active status + workspace-wide prefix.
+    # Scope: workspace_id + active status + workspace-wide prefix
+    # (owner segment wildcarded: workspace/%/%).
     assert "scripts.workspace_id" in sql
     assert "scripts.status" in sql
-    assert "like 'workspace/%%'" in sql
+    assert "like 'workspace/%%/%%'" in sql
     # Non-admin (default) narrows by visibility.
     assert "scripts.owner_user_id = 'u001'" in sql
     assert "scripts.visibility in ('workspace', 'public')" in sql
@@ -87,9 +88,10 @@ async def test_count_scripts_handles_null_result() -> None:
 
 
 async def test_count_scripts_workspace_wide_not_user_scoped() -> None:
-    """The prefix is workspace-wide (``workspace/%`` — no embedded user_id),
-    so different users count the same physical tree; the only per-user
-    difference is the non-admin visibility predicate (owner_user_id = me)."""
+    """The prefix is workspace-wide (``workspace/%/%`` — owner segment
+    wildcarded, no embedded user_id), so different users count the same
+    physical tree; the only per-user difference is the non-admin
+    visibility predicate (owner_user_id = me)."""
     captured = []
 
     mock_session = MagicMock()
@@ -104,8 +106,8 @@ async def test_count_scripts_workspace_wide_not_user_scoped() -> None:
     sql_bob = _compile(captured[-1]).lower()
 
     # Both count the same workspace-wide subtree.
-    assert "like 'workspace/%%'" in sql_alice
-    assert "like 'workspace/%%'" in sql_bob
+    assert "like 'workspace/%%/%%'" in sql_alice
+    assert "like 'workspace/%%/%%'" in sql_bob
     # Neither embeds the user_id in the path prefix.
     assert "workspace/alice/%" not in sql_alice
     assert "workspace/bob/%" not in sql_bob
@@ -129,7 +131,7 @@ async def test_count_scripts_admin_skips_visibility_filter() -> None:
     )
     assert result["data"] == {"total": 42}
     sql = _compile(captured[0]).lower()
-    assert "like 'workspace/%%'" in sql
+    assert "like 'workspace/%%/%%'" in sql
     # visibility / owner_user_id still appear in the SELECT projection, but
     # the visibility WHERE predicate must be absent for admins.
     assert "scripts.visibility in ('workspace', 'public')" not in sql