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>

steward/templates/hosts/form.html

@@ -1,30 +1,42 @@
 {% extends "base.html" %}
-{% from "_macros.html" import crumbs %}
-{% block title %}{% if host %}Edit Host{% else %}New Host{% endif %} — Steward{% endblock %}
-{% block breadcrumb %}{{ crumbs([("Hosts", "/hosts/"), (("Edit " ~ host.name) if host else "New host", "")]) }}{% endblock %}
+{% from "_macros.html" import crumbs, page_header %}
+{# Add a host (host is none) or edit one; `values` holds what was typed when
+   an error sends the form back. Laid out like the add-monitor form (#5283). #}
+{% block title %}{{ "Edit " ~ host.name if host else "Add host" }} — Steward{% endblock %}
+{% block breadcrumb %}
+{%- if host -%}
+{{ crumbs([("Hosts", "/hosts/"), (host.name, "/hosts/" ~ host.id), ("Edit", "")]) }}
+{%- else -%}
+{{ crumbs([("Hosts", "/hosts/"), ("Add host", "")]) }}
+{%- endif -%}
+{% endblock %}
 {% block content %}
-<div style="max-width:560px;margin:2rem auto;">
-    <h1 class="page-title">{% if host %}Edit Host{% else %}Add Host{% endif %}</h1>
-    <div class="card">
-        <form method="post" action="{% if host %}/hosts/{{ host.id }}{% else %}/hosts/{% endif %}">{{ csrf_field() }}
-            <div class="form-group">
-                <label>Display Name</label>
-                <input type="text" name="name" value="{{ host.name if host else '' }}" required autofocus>
-            </div>
-            <div class="form-group">
-                <label>Address (hostname or IP)</label>
-                <input type="text" name="address" value="{{ host.address if host else '' }}" required>
-            </div>
-            <div style="display:flex;gap:1rem;margin-top:1.5rem;">
-                <button type="submit" class="btn">{% if host %}Save{% else %}Add Host{% endif %}</button>
-                <a href="{% if host %}/hosts/{{ host.id }}{% else %}/hosts/{% endif %}" class="btn btn-ghost">Cancel</a>
-            </div>
-        </form>
+{% set v = values or {} %}
+{{ page_header("Edit host" if host else "Add host") }}
+
+<div class="card" style="max-width:760px;">
+  {% if error %}<p class="field-error" role="alert">{{ error }}</p>{% endif %}
+  <form method="post" action="{{ '/hosts/' ~ host.id if host else '/hosts/' }}" style="display:grid;gap:0.6rem;">{{ csrf_field() }}
+    <div style="display:grid;grid-template-columns:repeat(auto-fill,minmax(220px,1fr));gap:0.6rem;align-items:end;">
+      <div>
+        <label class="field-label" for="h-name">Name <span class="tone-crit" aria-hidden="true">*</span></label>
+        <input type="text" id="h-name" name="name" value="{{ v.name if v.name is defined else (host.name if host else '') }}"
+               placeholder="nas, web-1, …" autocomplete="off" required autofocus class="input">
+      </div>
+      <div>
+        <label class="field-label" for="h-address">Address</label>
+        <input type="text" id="h-address" name="address" value="{{ v.address if v.address is defined else (host.address if host else '') }}"
+               placeholder="hostname or IP; empty resolves by name" autocomplete="off" class="input">
+      </div>
     </div>
-    <p style="color:var(--text-muted);font-size:0.82rem;margin-top:1rem;text-align:center;">
-        {% if host %}Monitors, agent, Ansible target, and playbook runs live on the
-        <a href="/hosts/{{ host.id }}">host page</a>.{% else %}
-        After adding, attach ping / DNS / HTTP monitors from the host page.{% endif %}
+    <p class="field-hint" style="margin:0;">
+      {% if host %}Renaming carries the host's agent and container history, and the alert rules on it, to the new name.
+      {% else %}Next, on the host's page: add monitors, install its agent, and link an Ansible target.{% endif %}
     </p>
+    <div style="display:flex;gap:0.5rem;">
+      <button type="submit" class="btn btn-sm">{{ "Save" if host else "Add host" }}</button>
+      <a href="{{ '/hosts/' ~ host.id if host else '/hosts/' }}" class="btn btn-sm btn-ghost">Cancel</a>
+    </div>
+  </form>
 </div>
 {% endblock %}