Add Nav-I dashboard section with restore-as conflict resolution

- Create Nav-I top-level section in dashboard navigation
- Move Deleted Contacts from Knowledge subnav to Nav-I
- Add Nav-I landing page with card grid (deleted count, API keys stub)
- Add /nav-i/api-keys placeholder page
- Add restore-as endpoint for Home/Work conflict resolution
- Conflict modal in deleted contacts template for label rename on restore

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

templates/base.html

@@ -21,6 +21,7 @@
     <a href="/peertube"{% if domain == 'peertube' %} class="active"{% endif %}>PeerTube</a>
     <a href="/kiwix"{% if domain == 'kiwix' %} class="active"{% endif %}>Kiwix</a>
     <a href="/search"{% if domain == 'search' %} class="active"{% endif %}>Search</a>
+    <a href="/nav-i"{% if domain == 'navi' %} class="active"{% endif %}>Nav-I</a>
     <a href="/settings/keys"{% if domain == 'settings' %} class="active"{% endif %}>Settings</a>
 </div>
 {% if subnav %}