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>

static/daybook.css

@@ -990,6 +990,28 @@ kbd {
   word-break: break-all;
 }
 
+.about-head {
+  align-items: center;
+  display: flex;
+  gap: 1rem;
+  margin-bottom: 1.2rem;
+}
+
+.about-head h2 {
+  margin: 0;
+}
+
+.about-logo {
+  height: 3rem;
+  width: auto;
+}
+
+.about-version {
+  color: var(--muted);
+  font-size: 0.9rem;
+  margin: 0.15rem 0 0;
+}
+
 .keep-button.kept {
   background: var(--success-bg);
   border-color: var(--success-border);