feat(hosts): a host's health tiles span the card and the gaps match; Add host is a dialog on the list (#5290, #5291)

#5290 "Host page: the health tiles span the card's width; even spacing above Ansible":
the four tiles take equal quarters (halves on a phone) and their sparklines stretch
across them; the Monitors + Agent row drops the Agent card's own margin, so the gap
above Ansible is 1rem like every other.

#5291 "Add host opens as a dialog over the Hosts list": a native <dialog> on /hosts/,
opened by Add host or /hosts/?add=1. A name clash re-renders the list with it open,
the error and what was typed. GET /hosts/new is gone; hosts/form.html is Edit only.

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

steward/templates/hosts/form.html

@@ -1,41 +1,34 @@
 {% extends "base.html" %}
 {% 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 %}
+{# Edit a host; `values` holds what was typed when a clash sends the form back.
+   Adding one is a dialog on the Hosts list (#5291). #}
+{% block title %}Edit {{ host.name }} — Steward{% endblock %}
+{% block breadcrumb %}{{ crumbs([("Hosts", "/hosts/"), (host.name, "/hosts/" ~ host.id), ("Edit", "")]) }}{% endblock %}
 {% block content %}
 {% set v = values or {} %}
-{{ page_header("Edit host" if host else "Add host") }}
+{{ page_header("Edit 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() }}
+  <form method="post" action="/hosts/{{ host.id }}" 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 '') }}"
+        <input type="text" id="h-name" name="name" value="{{ v.name if v.name is defined else host.name }}"
                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 '') }}"
+        <input type="text" id="h-address" name="address" value="{{ v.address if v.address is defined else host.address }}"
                placeholder="hostname or IP; empty resolves by name" autocomplete="off" class="input">
       </div>
     </div>
     <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 %}
+      Renaming carries the host's agent and container history, and the alert rules on it, to the new name.
     </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>
+      <button type="submit" class="btn btn-sm">Save</button>
+      <a href="/hosts/{{ host.id }}" class="btn btn-sm btn-ghost">Cancel</a>
     </div>
   </form>
 </div>