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/_topbar.html

@@ -12,6 +12,7 @@
     <div class="user-menu-dropdown" hidden data-user-menu>
       <a href="{% url 'settings-account' %}">Settings</a>
       <a href="{% url 'settings-demo-data' %}">Demo Data</a>
+      <a href="{% url 'settings-about' %}">About</a>
       <button type="button" data-theme-toggle>Dark mode</button>
       <form method="post" action="{% url 'logout' %}">{% csrf_token %}<button type="submit">Log out</button></form>
     </div>