feat: role-based ACL + admin management UI

Backend:
- Add acl.ts with requireAuth/requireRole/requireOwnerOrAdmin helpers
- Gate premium videos from unauthenticated users in videos query/resolver
- Fix updateVideoPlay to verify ownership before updating
- Add admin mutations: adminListUsers, adminUpdateUser, adminDeleteUser
- Add admin mutations: createVideo, updateVideo, deleteVideo, setVideoModels, adminListVideos
- Add admin mutations: createArticle, updateArticle, deleteArticle, adminListArticles
- Add deleteComment mutation (owner or admin only)
- Add AdminUserListType to GraphQL types
- Fix featured filter on articles query

Frontend:
- Install marked for markdown rendering
- Add /admin/* section with sidebar layout and admin-only guard
- Admin users page: paginated table with search, role filter, inline role change, delete
- Admin videos pages: list, create form, edit form with file upload and model assignment
- Admin articles pages: list, create form, edit form with split-pane markdown editor
- Add admin nav link in header (desktop + mobile) for admin users
- Render article content through marked in magazine detail page
- Add all admin GraphQL service functions to services.ts

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pnpm-lock.yaml

@@ -166,6 +166,9 @@ importers:
       javascript-time-ago:
         specifier: ^2.6.4
         version: 2.6.4
+      marked:
+        specifier: ^17.0.4
+        version: 17.0.4
       media-chrome:
         specifier: ^4.18.0
         version: 4.18.0(react@19.2.0)
@@ -2663,6 +2666,11 @@ packages:
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+  marked@17.0.4:
+    resolution: {integrity: sha512-NOmVMM+KAokHMvjWmC5N/ZOvgmSWuqJB8FoYI019j4ogb/PeRMKoKIjReZ2w3376kkA8dSJIP8uD993Kxc0iRQ==}
+    engines: {node: '>= 20'}
+    hasBin: true
+
   mdn-data@2.0.28:
     resolution: {integrity: sha512-aylIc7Z9y4yzHYAJNuESG3hfhC+0Ibp/MAMiaOZgNv4pmEdFyfZhhhny4MNiAfWdBQ1RQ2mfDWmM1x8SvGyp8g==}
 
@@ -5557,6 +5565,8 @@ snapshots:
     dependencies:
       '@jridgewell/sourcemap-codec': 1.5.5
 
+  marked@17.0.4: {}
+
   mdn-data@2.0.28: {}
 
   mdn-data@2.12.2: {}