Add host welcome/reset emails, email field, and /host URL; v2.0.7

- Host accounts now have an optional email field
- Creating a host with an email sends a welcome email with the portal
  URL, username, and password via Resend
- Resetting a password also emails the new credentials if the host
  has an email on file; admin sees a confirmation either way
- Admin panel shows email column and confirmation messages
- Portal URL changed from /host-upload to /host

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

src/App.tsx

@@ -3140,7 +3140,7 @@ export default function App() {
       <Route path="/subscribe" element={<SubscribePage />} />
       <Route path="/subscribe/thanks" element={<SubscribeThankYouPage />} />
       <Route path="/certificate/:token" element={<PublicCertificatePage />} />
-      <Route path="/host-upload" element={<NuggetsHostPortal />} />
+      <Route path="/host" element={<NuggetsHostPortal />} />
       <Route path="/admin" element={<AdminShell content={content} onSave={setContent} />} />
       <Route path="/preview" element={<PreviewPage />} />
       <Route