Add contact form inbox to admin portal; v2.0.25

- New Inbox view in the Audience nav group shows all contact form submissions
- Filter by Unread / All / Archived with a search bar for name, email, or message
- Click any message to open a detail pane with full text, metadata, and a Reply via Email link
- Archive / Unarchive button to clear messages without deleting them
- Unread badge on the Inbox nav item; dashboard card now links directly to Inbox
- Added PATCH /api/admin-contact-submissions/:id to persist archived state

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

server/routes/contact.js

@@ -358,6 +358,21 @@ export function register(app) {
     res.json({ submissions: state.contactSubmissions.slice(0, 300) })
   })
 
+  app.patch('/api/admin-contact-submissions/:id', requireAdminAuth, (req, res) => {
+    const { id } = req.params
+    const { archived } = req.body ?? {}
+    if (typeof archived !== 'boolean') {
+      res.status(400).json({ message: 'archived must be a boolean.' }); return
+    }
+    const idx = state.contactSubmissions.findIndex(s => s.id === id)
+    if (idx === -1) {
+      res.status(404).json({ message: 'Submission not found.' }); return
+    }
+    state.contactSubmissions[idx] = { ...state.contactSubmissions[idx], archived }
+    queueContactSubmissionsWrite()
+    res.json({ ok: true, submission: state.contactSubmissions[idx] })
+  })
+
   app.get('/api/admin-subscribers', requireAdminAuth, (_req, res) => {
     const seen = new Set()
     const subscribers = state.contactSubmissions