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/layout.html

@@ -0,0 +1,22 @@
+{{define "layout"}}<!doctype html>
+<html lang="en">
+<head>
+  <meta charset="utf-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1">
+  <title>{{.Title}} · package-updater</title>
+  <link rel="stylesheet" href="/static/app.css">
+  <script src="/static/htmx.min.js"></script>
+  <script src="/static/htmx-ext-sse.js"></script>
+</head>
+<body hx-headers='{"X-CSRF-Token": "{{.CSRF}}"}' hx-ext="sse" sse-connect="/events">
+  <nav>
+    <a href="/">Services</a>
+    <a href="/agents">Agents</a>
+    <form method="post" action="/auth/logout">
+      <input type="hidden" name="csrf_token" value="{{.CSRF}}">
+      <button type="submit">Log out</button>
+    </form>
+  </nav>
+  <main>{{template "content" .}}</main>
+</body>
+</html>{{end}}