feat(web): read-only dashboard app + ci web serve (W4)

src/ci_orchestrator/web/templates/partials/cache.html

@@ -0,0 +1,15 @@
+<div id="cache-partial">
+  <h2>Cargo cache</h2>
+  {% if cache %}
+  <dl>
+    <dt>Root</dt><dd><code>{{ cache.root }}</code></dd>
+    <dt>Total size</dt><dd>{{ cache.total_bytes }} bytes</dd>
+    <dt>Entries</dt><dd>{{ cache.entry_count }}</dd>
+    <dt>Oldest entry age</dt>
+    <dd>{{ cache.oldest_age_days ~ " day(s)" if cache.oldest_age_days is not none else "-" }}</dd>
+    <dt>Retention</dt><dd>{{ cache.retention_days }} day(s)</dd>
+  </dl>
+  {% else %}
+  <p class="notice notice-warn">Cargo cache status unavailable.</p>
+  {% endif %}
+</div>