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

devplacepy/routers/docs/pages.py

@@ -51,6 +51,12 @@ DOCS_PAGES = [
         "kind": "prose",
         "section": SECTION_GENERAL,
     },
+    {
+        "slug": "getting-started-vibing",
+        "title": "Get started with vibing",
+        "kind": "prose",
+        "section": SECTION_GENERAL,
+    },
     {
         "slug": "feed",
         "title": "The feed",
@@ -308,6 +314,13 @@ DOCS_PAGES = [
         for page in api_doc_pages()
     ],
     # Administration - operational guides (admins only)
+    {
+        "slug": "devii-admin",
+        "title": "Devii for admins",
+        "kind": "prose",
+        "admin": True,
+        "section": SECTION_ADMIN,
+    },
     {
         "slug": "media-moderation",
         "title": "Media moderation",