feat: add build info (commit SHA + deploy timestamp) to health endpoint and admin sidebar

- deploy.sh writes .build-info with commit SHA and timestamp after git pull
- /health endpoint now returns version, commit, and deployed_at fields
- Admin sidebar footer shows version and commit SHA
- Hetzner docs updated: runner --config flag, swap, and runner timeout

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/templates/admin/partials/sidebar.html

@@ -101,8 +101,18 @@
    DESKTOP SIDEBAR
    ============================================================================ #}
 
-<aside class="z-20 hidden w-64 overflow-y-auto bg-white dark:bg-gray-800 md:block flex-shrink-0">
-    {{ sidebar_content() }}
+<aside class="z-20 hidden w-64 overflow-y-auto bg-white dark:bg-gray-800 md:block flex-shrink-0 flex flex-col">
+    <div class="flex-1">
+        {{ sidebar_content() }}
+    </div>
+    <div class="px-6 py-3 border-t border-gray-200 dark:border-gray-700">
+        <p class="text-[10px] font-mono text-gray-400 dark:text-gray-600">
+            v{{ config.version }}
+            {% if config.commit %}
+                · <span title="Deployed {{ config.deployed_at or '' }}">{{ config.commit }}</span>
+            {% endif %}
+        </p>
+    </div>
 </aside>
 
 {# ============================================================================