feat: restrict backup archive download to primary admin and hide admin-hidden projects from other admins

- Add `get_admin_uids()` and `get_primary_admin_uid()` to database.py for resolving the earliest-created admin
- Modify `can_view_project()` in content.py so a project hidden by an admin is invisible to other admins (both web UI and REST API)
- Update `_download_url()` and `_backup_payload()` in admin/backups.py to accept a `can_download` flag, gating the download endpoint with `is_primary_admin()`
- Remove `role` from `_user_facts()` in docs_live.py to avoid leaking admin status in live docs
- Update doc summaries in docs_api.py to reflect the new admin-visibility and backup-download semantics

tests/api/project/visibility.py

@@ -78,6 +78,16 @@ def _list_slugs(key=None, user_uid=None):
     params = {"user_uid": user_uid} if user_uid else None
     r = requests.get(f"{BASE_URL}/projects", headers=_h_project_visibility(key), params=params)
     return [p["slug"] for p in r.json()["projects"]]
+def _detail_status(key, slug):
+    return requests.get(
+        f"{BASE_URL}/projects/{slug}", headers=_h_project_visibility(key)
+    ).status_code
+def _file_raw_status(key, slug, path):
+    return requests.get(
+        f"{BASE_URL}/projects/{slug}/files/raw",
+        headers=_h_project_visibility(key),
+        params={"path": path},
+    ).status_code
 
 
 def test_private_project_hidden_from_guest_listing(app_server):
@@ -101,6 +111,29 @@ def test_private_project_visible_to_admin(app_server):
     assert slug in _list_slugs(key=admin_key, user_uid=owner_uid)
 
 
+def test_admin_private_hidden_from_other_admin(app_server):
+    _, owner_uid, owner_key = _make_admin_project_visibility()
+    _, _, other_admin_key = _make_admin_project_visibility()
+    slug = _create_project_project_visibility(
+        owner_key, "Admin Hidden", is_private=True
+    )["slug"]
+    assert slug not in _list_slugs(key=other_admin_key, user_uid=owner_uid)
+    assert _detail_status(other_admin_key, slug) == 404
+    assert _file_raw_status(other_admin_key, slug, "missing.txt") == 404
+    assert slug in _list_slugs(key=owner_key, user_uid=owner_uid)
+    assert _detail_status(owner_key, slug) == 200
+
+
+def test_member_private_still_visible_to_admin(app_server):
+    _, owner_uid, owner_key = _signup_project_visibility()
+    _, _, admin_key = _make_admin_project_visibility()
+    slug = _create_project_project_visibility(
+        owner_key, "Member Hidden", is_private=True
+    )["slug"]
+    assert slug in _list_slugs(key=admin_key, user_uid=owner_uid)
+    assert _detail_status(admin_key, slug) == 200
+
+
 def test_toggle_private_then_public(app_server):
     _, owner_uid, key = _signup_project_visibility()
     slug = _create_project_project_visibility(key, "Toggle Privacy")["slug"]