Split internal/web into subpackages before domain-admin growth.

Lay out view, auth, validate, and handlers under internal/web while keeping
the cmd/panel API unchanged; update roadmap and changelog for web-split closure.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/web/view/templates/account.html

@@ -0,0 +1,68 @@
+{{define "content"}}
+<h1>Settings</h1>
+
+{{if .Flash}}<div class="flash">{{.Flash}}</div>{{end}}
+
+<div class="card narrow">
+  <h2>Panel credentials</h2>
+  <p class="muted">These are the credentials for this control panel only.
+  Applications keep their own logins and passwords, which are not affected.</p>
+  {{if .Error}}<p class="error">{{.Error}}</p>{{end}}
+  <form method="post" action="/account">
+    <label for="username">Username</label>
+    <input id="username" name="username" autocomplete="username"
+           autocapitalize="none" spellcheck="false" value="{{.FormUsername}}" required>
+
+    <label for="current_password">Current password</label>
+    <input id="current_password" name="current_password" type="password"
+           autocomplete="current-password" required>
+
+    <label for="new_password">New password</label>
+    <input id="new_password" name="new_password" type="password" autocomplete="new-password">
+
+    <label for="new_password_confirm">Confirm new password</label>
+    <input id="new_password_confirm" name="new_password_confirm" type="password" autocomplete="new-password">
+
+    <h3>DMARC aggregate reports</h3>
+    <p class="muted">Optional default <code>rua=</code> address for every sending
+    domain (can be overridden per domain). Use a mailbox on a domain that
+    receives inbound mail. SelfPost is send-only today; a future release will
+    be able to receive reports in the panel itself.</p>
+
+    <label for="dmarc_report_email">Default report address</label>
+    <input id="dmarc_report_email" name="dmarc_report_email" type="email"
+           autocomplete="email" autocapitalize="none" spellcheck="false"
+           value="{{.FormDMARCEmail}}" placeholder="reports@your-mail-domain.com">
+
+    {{if .FormDMARCEmail}}
+    <p class="muted">When <code>rua=</code> points at another domain, that hub
+    domain must publish a report-authorisation record so receivers will deliver
+    the XML aggregates.</p>
+
+    <label>Report authorization — host / name</label>
+    <div class="code-row">
+      <span class="code">{{.ReportAuthName}}</span>
+      <button type="button" class="copy">Copy</button>
+    </div>
+
+    <label>Report authorization — value</label>
+    <div class="code-row">
+      <span class="code">{{.ReportAuthExample}}</span>
+      <button type="button" class="copy">Copy</button>
+    </div>
+
+    {{if .ReportAuthDNS.Status}}
+    <label>Report authorization DNS <span class="st st-{{.ReportAuthDNS.Status}}">{{.ReportAuthDNS.Status}}</span></label>
+    <p class="{{if eq .ReportAuthDNS.Status "ok"}}muted{{else}}error{{end}}">{{.ReportAuthDNS.Detail}}</p>
+    {{if .ReportAuthDNS.Records}}<span class="code">{{range .ReportAuthDNS.Records}}{{.}}
+{{end}}</span>{{end}}
+    {{end}}
+    {{end}}
+
+    <button type="submit">Save changes</button>
+  </form>
+  <p class="muted">Leave both new-password fields empty to change the username
+  or DMARC address only. Changing the password signs out every other session;
+  this one stays signed in.</p>
+</div>
+{{end}}