feat: host inventory (agent.inventory), host detail page, UI columns

Store hardware/software snapshots on hosts; warn on hardware changes. Host card from Hosts list. Add agent version column to Events/Overview; rename Hosts table columns and sort by status.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/views/EventsView.vue

@@ -33,6 +33,7 @@
           <th>Время</th>
           <th>Хост</th>
           <th>Имя сервера</th>
+          <th>Версия агента</th>
           <th>Severity</th>
           <th>Type</th>
           <th>Title</th>
@@ -46,6 +47,7 @@
           <td>{{ formatDt(e.occurred_at) }}</td>
           <td>{{ e.hostname }}</td>
           <td>{{ formatServerName(e.display_name) }}</td>
+          <td>{{ e.product_version || "—" }}</td>
           <td :class="'sev-' + e.severity">{{ e.severity }}</td>
           <td><code>{{ e.type }}</code></td>
           <td>{{ e.title }}</td>