feat(host_agent): agent reports its primary IP; mirror into Host.address (task 274)

The agent now detects its own primary non-loopback IP (UDP-socket trick, no
packets sent) and sends it in the metadata bag; bumps AGENT_VERSION 1.0.0->1.1.0
and re-detects on SIGHUP. The server persists it on HostAgentRegistration.host_ip
and mirrors it into Host.address ONLY when that field is blank — an admin-typed
address is never overwritten. The reported IP shows in the settings table so
admins can see drift regardless.

- agent.py: detect_primary_ip(); host_ip in collect_metadata(); refresh on reload
- routes.py: pure pick_host_address() helper; ingest persists host_ip + mirrors
- models.py + migration host_agent_002_host_ip: new String(45) column
- settings_list.html: Reported IP column
- plugin.yaml: 1.0.0 -> 1.1.0
- tests: pick_host_address (fill-when-blank / never-clobber / no-op),
  detect_primary_ip (never raises, non-loopback), metadata carries host_ip

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

plugins/host_agent/templates/settings_list.html

@@ -32,7 +32,7 @@
   <table class="table">
     <thead>
       <tr>
-        <th>Host</th><th>Agent version</th><th>Distro</th>
+        <th>Host</th><th>Reported IP</th><th>Agent version</th><th>Distro</th>
         <th>Last seen</th><th class="td-actions">Actions</th>
       </tr>
     </thead>
@@ -40,6 +40,7 @@
       {% for item in registrations %}
       <tr>
         <td>{{ item.host.name if item.host else item.reg.host_id }}</td>
+        <td>{{ item.reg.host_ip or "—" }}</td>
         <td>{{ item.reg.agent_version or "—" }}</td>
         <td>{{ item.reg.distro or "—" }}</td>
         <td>{{ item.reg.last_seen_at.strftime("%Y-%m-%d %H:%M:%S") if item.reg.last_seen_at else "never" }}</td>
@@ -57,7 +58,7 @@
         </td>
       </tr>
       {% else %}
-      <tr><td colspan="5" class="empty">No hosts registered. Add one above.</td></tr>
+      <tr><td colspan="6" class="empty">No hosts registered. Add one above.</td></tr>
       {% endfor %}
     </tbody>
   </table>