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/navi/api_keys.html

@@ -0,0 +1,8 @@
+{% extends "base.html" %}
+{% block content %}
+<h3 style="color:var(--orange);margin-bottom:16px;">API Keys</h3>
+<div class="panel">
+    <p class="text-dim">Per-user API key management is coming soon.</p>
+    <p class="text-dim" style="margin-top:8px;font-size:11px;">This will allow generating keys for programmatic access to the Navi contacts API.</p>
+</div>
+{% endblock %}