feat(master): htmx UI with live service overview and agent management

Vendored static assets (sha256):
e209dda5c8235479f3166defc7750e1dbcd5a5c1808b7792fc2e6733768fb447  htmx.min.js (htmx.org@2.0.4)
83eca6fa0611fe2b0bf1700b424b88b5eced38ef448ef9760a2ea08fbc875611  htmx-ext-sse.js (htmx-ext-sse@2.2.2)

internal/master/web/templates/agents.html

@@ -0,0 +1,38 @@
+{{define "content"}}
+<h1>Agents</h1>
+<form method="post" action="/agents" class="inline">
+  <input type="hidden" name="csrf_token" value="{{.CSRF}}">
+  <label>Name <input name="name" required placeholder="node-2"></label>
+  <button type="submit">Add agent</button>
+</form>
+{{if .Error}}<p class="error">{{.Error}}</p>{{end}}
+<div id="agents" hx-get="/fragments/agents" hx-trigger="sse:agents" hx-swap="innerHTML">
+  {{template "agents" .}}
+</div>
+{{end}}
+
+{{define "agents"}}
+<table>
+  <thead><tr><th>Name</th><th>Hostname</th><th>State</th><th>Version</th><th>Swarm manager</th><th>Last seen</th><th></th></tr></thead>
+  <tbody>
+  {{range .Agents}}
+    <tr>
+      <td>{{.Name}}</td>
+      <td>{{.Hostname}}</td>
+      <td>{{if .RevokedAt}}<span class="status status-stopped">revoked</span>{{else if .Online}}<span class="status status-running">online</span>{{else}}<span class="status status-degraded">offline</span>{{end}}</td>
+      <td>{{.AgentVersion}}</td>
+      <td>{{if .SwarmManager}}yes{{end}}</td>
+      <td>{{with .LastSeenAt}}{{.Format "2006-01-02 15:04"}}{{end}}</td>
+      <td>{{if not .RevokedAt}}
+        <form method="post" action="/agents/{{.ID}}/revoke" onsubmit="return confirm('Revoke {{.Name}}? It is disconnected immediately and must be added again to come back.')">
+          <input type="hidden" name="csrf_token" value="{{$.CSRF}}">
+          <button type="submit">Revoke</button>
+        </form>
+      {{end}}</td>
+    </tr>
+  {{else}}
+    <tr><td colspan="7">No agents yet.</td></tr>
+  {{end}}
+  </tbody>
+</table>
+{{end}}