feat(homeassistant): its page offers the metrics scrape under the same sign-in, so one user covers everything (#6744)

A Prometheus target's token_from names the plugin that supplies its token at each
scrape. Read its metrics makes the target; Use this sign-in moves one at that address
across, keeping its name, filters and history. A refusal stops the connection, so one
Try again or sign-in starts everything, and the sign-in is only sent to its own address.
A 404 says how to turn on Home Assistant's Prometheus integration, as Steward doesn't
change Home Assistant. Refused also joins the volatile columns a backup check ignores.

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

plugins/homeassistant/templates/homeassistant/form.html

@@ -23,7 +23,7 @@
     <label style="display:flex;gap:0.5rem;align-items:center;cursor:pointer;margin-bottom:0.9rem;">
       <input type="checkbox" name="verify_tls" value="on"{% if verify_tls %} checked{% endif %}> Check its HTTPS certificate
     </label>
-    <p class="tone-warn"><strong>Steward stores a credential with the same access as the user who signs in.</strong> Home Assistant has no narrower permission, so an administrator's credential can do anything that administrator can, including controlling every device. Steward only uses it to read status, take backups and install updates.</p>
+    <p class="tone-warn"><strong>Steward stores a credential with the same access as the user who signs in.</strong> Home Assistant has no narrower permission, so an administrator's credential can do anything that administrator can, including controlling every device. Steward only uses it to read status and metrics, take backups and install updates.</p>
     <p class="field-hint"><strong>We recommend a service account:</strong> a Home Assistant user made just for Steward (Settings → People → Add person). What Steward does then appears under its own name in Home Assistant's logs, so it's easy to tell apart from what people do.</p>
     <p class="field-hint" style="margin-bottom:0;">Installing updates needs an administrator. With any other user, Steward shows status only.</p>
   </section>
@@ -38,7 +38,7 @@
 <section class="card danger-zone" aria-labelledby="ha-remove">
   <div>
     <h2 id="ha-remove" class="section-title">Remove this connection</h2>
-    <p class="field-hint">Steward stops reading Home Assistant, forgets its credential and ends the sign-in there.</p>
+    <p class="field-hint">Steward stops reading Home Assistant, its metrics included, forgets its credential and ends the sign-in there.</p>
   </div>
   <form method="post" action="/plugins/homeassistant/connection/delete"
         data-confirm="Remove the Home Assistant connection? Steward stops reading it and forgets its credential.">{{ csrf_field() }}

plugins/homeassistant/templates/homeassistant/index.html

@@ -73,6 +73,22 @@
   {% if others %}<p class="field-hint" style="margin-bottom:0;">Waiting, for Home Assistant to install: {% for u in others %}{{ u.title }}{{ ", " if not loop.last }}{% endfor %}. Steward installs Core, OS and add-on updates only.</p>{% endif %}
 </section>
 
+{% if metrics %}
+<section class="card" aria-labelledby="ha-metrics">
+  <h2 id="ha-metrics" class="section-title">Metrics</h2>
+  {% if metrics.uses_sign_in %}
+  <p class="field-hint" style="margin-bottom:0;">{{ status_badge(metrics.reach) }} Read with this sign-in into the target <a href="/plugins/prometheus/targets/{{ metrics.id }}">{{ metrics.name }}</a>: {{ metrics.says }}{% if metrics.reach == 'up' %} {{ metrics.kept }} series kept.{% endif %}</p>
+  {% elif metrics.id %}
+  <p class="field-hint">The target <a href="/plugins/prometheus/targets/{{ metrics.id }}">{{ metrics.name }}</a> reads these with a token of its own: {{ metrics.says }}</p>
+  {% if admin %}<p class="field-hint">Use this sign-in instead, so one Home Assistant user covers everything. The target keeps its name, filters and history, and forgets its token.</p>
+  <form method="post" action="/plugins/homeassistant/metrics">{{ csrf_field() }}<button class="btn btn-sm" type="submit">Use this sign-in</button></form>{% endif %}
+  {% else %}
+  <p class="field-hint">Home Assistant's entity readings can be kept as metrics too, for charts and alert rules, with this sign-in and nothing else to set up.</p>
+  {% if admin %}<form method="post" action="/plugins/homeassistant/metrics">{{ csrf_field() }}<button class="btn btn-sm" type="submit">Read its metrics</button></form>{% endif %}
+  {% endif %}
+</section>
+{% endif %}
+
 {% if runs %}
 <section class="card" aria-labelledby="ha-runs">
   <h2 id="ha-runs" class="section-title">Updates run from Steward</h2>