feat(hosts): the Hosts list labels its figures and says how long; SLA tab gone; one place to add a host (#5279–#5283)

Hosts list:
- CPU and Memory are their own labelled columns (#5279); a silent
  agent's last readings are greyed, and Status says "agent silent for 7m".
- One uptime figure, 30 days, with 24h and 7d on hover. The SLA tab
  (/hosts/uptime) repeated it and is removed (#5280; one home per fact).
- Status is a word with how long ("Down for 12m"); host_status now carries
  down_since. Edit and Delete live on the host's page only (#5281).
- Figures are right-aligned with tabular digits (.table .num), not a
  monospace face.

Agent fleet (#5282): its add-host form is gone, so hosts are added only on
Hosts -> Add host. That form was also the only way to get a token for a
manual curl install, so that moves to the host's Agent card as "Install
manually" (POST /fleet/<host_id>/register), shown on the fleet page as
before. "Delete" there reads "Unregister".

Add host (#5283): laid out like the add-monitor form; a name clash comes
back inline with what was typed instead of a bare text 400; the address
is optional, as the host page already allowed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugins/host_agent/templates/panel.html

@@ -91,8 +91,7 @@
 
   {% elif not ansible_available %}
   <p style="color:var(--text-dim);font-size:0.85rem;">
-    Ansible isn't available, so the agent can't be deployed from here. Install it manually with the
-    <a href="/plugins/host_agent/fleet/">curl install command</a>.
+    Ansible isn't available, so the agent can't be deployed from here. Install it manually instead (below).
   </p>
 
   {% elif not managed_key_set %}
@@ -141,6 +140,16 @@
   </form>
   {% endif %}
 
+  {% if not reg and session.user_role == 'admin' %}
+  {# A manual install: no Ansible, no SSH. Issues this host's token and shows
+     the one-line install command on the fleet page, once (#5282). #}
+  <form method="post" action="/plugins/host_agent/fleet/{{ host.id }}/register"
+        style="display:flex;gap:0.6rem;align-items:center;flex-wrap:wrap;margin:0.75rem 0 0;">{{ csrf_field() }}
+    <span style="font-size:0.78rem;color:var(--text-muted);">Or by hand on the host:</span>
+    <button type="submit" class="btn btn-sm btn-ghost">Install manually</button>
+  </form>
+  {% endif %}
+
   {% if reg and session.user_role == 'admin' %}
   <form method="post" action="/plugins/host_agent/fleet/{{ host.id }}/delete" style="margin:0.75rem 0 0;"
         data-confirm="Clear this pending registration? Its token is discarded.">{{ csrf_field() }}