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>

plugins/host_agent/routes.py

@@ -690,7 +690,7 @@ async def host_vitals(host_id: str):
     # At-a-glance disk = the root filesystem (what people actually care about),
     # not the "worst" mount which is opaque. Worst stays on the full-metrics page.
     disk_root = (latest.get(host.name + ":/", {}) or {}).get("disk_used_pct")
-    sparks = {k: sparkline_svg(v) for k, v in series_raw.items()}
+    sparks = {k: sparkline_svg(v, height=24, fill_width=True) for k, v in series_raw.items()}
     # Normalize load by core count so it's comparable across hardware (load/core
     # as %). Cores derived from the per-core CPU sub-resources already collected.
     cores = sum(1 for k in latest if k.startswith(host.name + ":core"))

plugins/host_agent/templates/_host_vitals.html

@@ -18,7 +18,7 @@
       {%- if reg.agent_version %}{{ " · " if not stale }}agent v{{ reg.agent_version }}{% endif -%}
     </span>
   </div>
-  <div class="stat-strip" style="margin-bottom:0;">
+  <div class="stat-strip host-health-tiles" style="margin-bottom:0;">
     {{ stat_tile("CPU", pct(cpu), state=status_class(cpu, 'cpu'), hint=sparks.cpu|safe) }}
     {{ stat_tile("Memory", pct(mem), state=status_class(mem, 'mem'), hint=sparks.mem|safe) }}
     {{ stat_tile("Disk /", pct(disk_root), state=status_class(disk_root, 'disk'), hint=sparks.disk|safe) }}

plugins/host_agent/templates/settings_list.html

@@ -9,7 +9,7 @@
 <p style="color:var(--text-muted);font-size:0.84rem;margin:-0.4rem 0 1.25rem;">
   Bulk agent operations across your inventory. For a single host, use its
   <a href="/hosts/">host page</a>: provisioning, a manual install command and
-  metrics live there. New hosts are added with <a href="/hosts/new">Add host</a>.
+  metrics live there. New hosts are added with <a href="/hosts/?add=1">Add host</a>.
 </p>
 
 {% if new_token %}
@@ -54,7 +54,7 @@
         </td>
       </tr>
       {% else %}
-      <tr><td colspan="7" class="empty">No agents registered yet. <a href="/hosts/new">Add a host</a>, then install its agent from the host's page.</td></tr>
+      <tr><td colspan="7" class="empty">No agents registered yet. <a href="/hosts/?add=1">Add a host</a>, then install its agent from the host's page.</td></tr>
       {% endfor %}
     </tbody>
   </table>