Phase 7: monitoring UI — send log, queue, mail.log tail

Three HTMX-polled monitoring screens (spec 7.2.11-13): send log with
server-side domain/application filters and pagination, Postfix queue
(postqueue -p), and a mail.log tail. Fragment endpoints return HTML
snippets, not JSON (spec 7.1); all output is auto-escaped via
html/template (spec 7.6.7).

Adds store.QuerySendLog/CountSendLog/ListApplicationLogins,
postfix.Queue(), and logtail.TailLines (a point-in-time reverse read,
independent of the background follow loop). Verified on the dev server:
gofmt/vet/test green, docker build green, container e2e (filters,
60-row pagination, <script> escaping, real postqueue/mail.log output,
existing Reload button unaffected).

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

internal/web/templates/dashboard.html

@@ -3,6 +3,9 @@
   <h1>SelfPost</h1>
   <div class="actions muted">
     <span>{{.User}}</span>
+    <a href="/sendlog">Send log</a>
+    <a href="/queue">Queue</a>
+    <a href="/logtail">Log</a>
     <form class="inline" method="post" action="/reload">
       <button type="submit">Reload</button>
     </form>

internal/web/templates/logtail.html

@@ -0,0 +1,21 @@
+{{define "content"}}
+<div class="topbar">
+  <h1>Mail log</h1>
+  <div class="actions muted">
+    <span>{{.User}}</span>
+    <a href="/">Domains</a>
+    <a href="/sendlog">Send log</a>
+    <a href="/queue">Queue</a>
+    <form class="inline" method="post" action="/logout">
+      <button type="submit">Sign out</button>
+    </form>
+  </div>
+</div>
+
+<a class="back" href="/">&larr; Domains</a>
+
+<div class="card">
+  <h2>mail.log tail</h2>
+  {{template "logtail_body" .}}
+</div>
+{{end}}

internal/web/templates/logtail_body.html

@@ -0,0 +1,7 @@
+{{define "logtail_body"}}
+<div id="logtail-body" hx-get="/logtail/body" hx-trigger="every 5s" hx-swap="outerHTML">
+  {{if .Error}}<p class="error">{{.Error}}</p>{{end}}
+  <span class="code">{{if .Lines}}{{range .Lines}}{{.}}
+{{end}}{{else}}No log lines yet.{{end}}</span>
+</div>
+{{end}}

internal/web/templates/queue.html

@@ -0,0 +1,21 @@
+{{define "content"}}
+<div class="topbar">
+  <h1>Mail queue</h1>
+  <div class="actions muted">
+    <span>{{.User}}</span>
+    <a href="/">Domains</a>
+    <a href="/sendlog">Send log</a>
+    <a href="/logtail">Log</a>
+    <form class="inline" method="post" action="/logout">
+      <button type="submit">Sign out</button>
+    </form>
+  </div>
+</div>
+
+<a class="back" href="/">&larr; Domains</a>
+
+<div class="card">
+  <h2>postqueue -p</h2>
+  {{template "queue_body" .}}
+</div>
+{{end}}

internal/web/templates/queue_body.html

@@ -0,0 +1,6 @@
+{{define "queue_body"}}
+<div id="queue-body" hx-get="/queue/body" hx-trigger="every 5s" hx-swap="outerHTML">
+  {{if .Error}}<p class="error">{{.Error}}</p>{{end}}
+  <span class="code">{{if .Output}}{{.Output}}{{else}}Queue is empty.{{end}}</span>
+</div>
+{{end}}

internal/web/templates/sendlog.html

@@ -0,0 +1,37 @@
+{{define "content"}}
+<div class="topbar">
+  <h1>Send log</h1>
+  <div class="actions muted">
+    <span>{{.User}}</span>
+    <a href="/">Domains</a>
+    <a href="/queue">Queue</a>
+    <a href="/logtail">Log</a>
+    <form class="inline" method="post" action="/logout">
+      <button type="submit">Sign out</button>
+    </form>
+  </div>
+</div>
+
+<a class="back" href="/">&larr; Domains</a>
+
+<div class="card">
+  <h2>Filter</h2>
+  <form method="get" action="/sendlog">
+    <label for="domain">Domain</label>
+    <select id="domain" name="domain">
+      <option value="">All domains</option>
+      {{range .FilterDomains}}<option value="{{.}}" {{if eq . $.FilterDomain}}selected{{end}}>{{.}}</option>{{end}}
+    </select>
+    <label for="app">Application</label>
+    <select id="app" name="app">
+      <option value="">All applications</option>
+      {{range .FilterApps}}<option value="{{.}}" {{if eq . $.FilterApp}}selected{{end}}>{{.}}</option>{{end}}
+    </select>
+    <button type="submit">Filter</button>
+  </form>
+</div>
+
+<div class="card">
+  {{template "sendlog_rows" .}}
+</div>
+{{end}}

internal/web/templates/sendlog_rows.html

@@ -0,0 +1,32 @@
+{{define "sendlog_rows"}}
+<div id="sendlog-rows" hx-get="/sendlog/rows?domain={{.FilterDomain}}&app={{.FilterApp}}&p={{.Page}}"
+     hx-trigger="every 5s" hx-swap="outerHTML">
+  {{if .Rows}}
+  <table>
+    <thead>
+      <tr><th>Time</th><th>Domain</th><th>App</th><th>From</th><th>To</th><th>Subject</th><th>Status</th></tr>
+    </thead>
+    <tbody>
+      {{range .Rows}}
+      <tr>
+        <td class="muted">{{.CreatedAt.Format "2006-01-02 15:04:05"}}</td>
+        <td>{{.Domain}}</td>
+        <td>{{.AppLogin}}</td>
+        <td>{{.From}}</td>
+        <td>{{.To}}</td>
+        <td>{{.Subject}}</td>
+        <td>{{.Status}}</td>
+      </tr>
+      {{end}}
+    </tbody>
+  </table>
+  <p class="muted">
+    Page {{.Page}}{{if .LastPage}} of {{.LastPage}}{{end}}
+    {{if .HasPrev}} &middot; <a href="/sendlog?domain={{.FilterDomain}}&app={{.FilterApp}}&p={{.PrevPage}}">&larr; Newer</a>{{end}}
+    {{if .HasNext}} &middot; <a href="/sendlog?domain={{.FilterDomain}}&app={{.FilterApp}}&p={{.NextPage}}">Older &rarr;</a>{{end}}
+  </p>
+  {{else}}
+  <p class="muted">No messages logged yet.</p>
+  {{end}}
+</div>
+{{end}}