panel-notifications: Account, Server > Settings, Server > Health, help; e2e

The pages of the mockups accepted in 87fa0a4, built from the kit's partials
(written by a Sonnet agent into the working tree, reviewed here):

- Account: "Send me notifications" in the Profile form, saved with the
  profile; an unticked box is off.
- Server > Settings: the instance switch (box 03), and box 04 Notification
  mail with the DKIM and SPF records of the server's own name, drawn with the
  record partial of a domain's DNS page and checked in DNS. Sending rate
  limits are box 02 in the left column. A record that is not in place is
  tagged as a warning, not a failure: notifications are sent without it.
- Server > Health: card 06 Notification mail with the state of each record
  and a link to Settings, beside Configuration (07); part of the polled
  fragment; Re-check DNS forces it too. Overview does not run this check.
- help.go: the Notifications topic and the clauses in Settings and Your
  account, word for word with help.html.

If the server's key cannot be read the pages still render: the DKIM record
is left out and SPF is shown unchecked.

e2e: the administrator gets a mailbox behind the sink and the server's DKIM
record from Settings is published; the level-2 refusal of the next step must
then arrive as a notification from postmaster@mail.e2e.test, signed as that
name with the key Settings shows, and must not be a row of the Outbound log.
The rotation step now waits for Postfix to be running: it follows a step that
restarts the container, and logrotate's `postfix reload` failed in between.

On the test server, for this tree: go vet clean, go test ./... 23 packages
ok, make e2e ok (147 s); the notification reached the sink 28 s after the
refusal.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/web/view/templates/settings.html

@@ -1,6 +1,8 @@
 {{/* Server > Settings (mockup settings.html): what holds for the whole instance.
-     One form, one Save button; the rate limits are read-only facts. A user's own
-     name, e-mail, password and DMARC address are on Account (account.html). */}}
+     One form, one Save button; the rate limits are read-only facts, and the
+     records of the server's own name are the ones notifications are signed and
+     authorised with. A user's own name, e-mail, password and DMARC address are on
+     Account (account.html). */}}
 {{define "content"}}
 {{template "page_head" .Head}}
 {{if .Flash}}{{template "flash" .Flash}}{{end}}
@@ -19,15 +21,26 @@
       {{end}}
       {{template "body_close"}}
       {{template "box_close"}}
-    </div>
 
-    <div class="column is-6">
       {{template "box_open" .RateLimits}}
       {{template "body_open"}}
       {{template "facts" .RateFacts}}
       {{template "body_close"}}
       {{template "box_close"}}
     </div>
+
+    <div class="column is-6">
+      {{template "box_open" .Notifications}}
+      {{template "body_open"}}
+      <div class="field"><label class="checkbox"><input type="checkbox" name="notify"{{if .Notify}} checked{{end}}> Send notification e-mails</label>
+        <p class="help">{{template "inline" .NotifyNote}}</p></div>
+      {{template "body_close"}}
+      {{template "box_close"}}
+
+      {{template "box_open" .Mail}}
+      {{range .MailRecords}}{{template "dns_record" .}}
+      {{end}}{{template "box_close"}}
+    </div>
   </div>
   <div class="buttons"><button type="submit" class="button is-primary">Save settings</button></div>
 </form>