Add version (0.1.0) and a Settings -> About page

Single source of truth: __version__ in daybook_project/__init__.py, starting
at 0.1.0. Surfaced in two places from that constant:
- Settings -> About page (logo, name, version, description), in the settings
  nav and linked from the gear menu.
- GET /api/capabilities now includes "version", so the deploy agent / tester
  can confirm which version is actually running.

Release flow: bump __version__, commit, `git tag vX.Y.Z`, push tag, deploy.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

templates/artifacts/settings_base.html

@@ -30,6 +30,7 @@
       {% if request.user.is_superuser %}
         <a class="{% if active_section == 'users' %}selected{% endif %}" href="{% url 'settings-users' %}">Users</a>
       {% endif %}
+      <a class="{% if active_section == 'about' %}selected{% endif %}" href="{% url 'settings-about' %}">About</a>
     </nav>
     <section class="settings-panel">
       {% if messages %}