Initial import: nasmon health monitor, split out of home_nas

Go service (nasmon/) plus nfpm packaging (packaging/), carried over from
the home_nas monorepo. Adds rpm packaging alongside the existing deb
build (Fedora/RHEL/Rocky dependency names via nfpm overrides, per-format
systemd unit path, dpkg+rpm-compatible maintainer scripts) and a Gitea
Actions workflow that builds both formats on every push.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

internal/web/templates/layout.html

@@ -0,0 +1,38 @@
+{{define "layout"}}<!doctype html>
+<html lang="en">
+<head>
+<meta charset="utf-8">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<title>{{.Title}} · nasmon</title>
+<link rel="stylesheet" href="/static/app.css">
+<link rel="icon" href="data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 16 16'%3E%3Crect width='16' height='16' rx='3' fill='%232d7ff9'/%3E%3C/svg%3E">
+</head>
+<body data-page="{{.Page}}">
+<header class="top">
+  <a class="brand" href="/">nasmon</a>
+  <nav>
+    <a href="/" {{if eq .Page "dashboard"}}class="on"{{end}}>Dashboard</a>
+    <a href="/zfs" {{if eq .Page "zfs"}}class="on"{{end}}>ZFS</a>
+    <a href="/shares" {{if eq .Page "shares"}}class="on"{{end}}>Shares</a>
+    <a href="/alerts" {{if eq .Page "alerts"}}class="on"{{end}}>Alerts{{if .Alerts}} <span class="badge crit">{{.Alerts}}</span>{{end}}</a>
+    <a href="/settings" {{if eq .Page "settings"}}class="on"{{end}}>Settings</a>
+  </nav>
+  <span class="refresh" id="refresh-state" title="auto-refresh"></span>
+</header>
+<main id="content">{{template "content" .}}</main>
+<script src="/static/app.js"></script>
+</body>
+</html>{{end}}
+
+{{define "flash"}}{{if .Flash}}<div class="flash ok">{{.Flash}}</div>{{end}}{{if .Error}}<div class="flash crit">{{.Error}}</div>{{end}}{{end}}
+
+{{define "alertlist"}}{{if .}}
+<section class="card alerts-open">
+  <h2>Open alerts</h2>
+  {{range .}}<div class="alert {{.Level}}">
+    <form method="post" action="/alerts/{{.ID}}/ack" class="x-form"><button type="submit" class="x" title="Acknowledge: hide until it changes or resolves">&times;</button></form>
+    <div class="alert-title"><span class="badge {{.Level}}">{{.Level}}</span> {{.Title}}</div>
+    <pre class="alert-detail">{{.Detail}}</pre>
+    <div class="muted">since {{dt .OpenedAt}}</div>
+  </div>{{end}}
+</section>{{end}}{{end}}