panel-redesign: Help with seventeen topics; every box links to its own

Follows the design commit before it. Written by Sonnet, reviewed by
Opus.

  - view/help.go, templates/help.html: the mockup's topics, texts, ids
    and menu. The page shows the groups the reader's menu shows:
    Overview and Server for the global role, Outbound and Inbound by
    reach (Inbound only with the feature on), Account for everyone;
    boxes are numbered as shown.
  - Box.Help set on the boxes the mockups mark; the inbound MX box has
    its link again.
  - TestEveryHelpLinkLandsOnATopic also fails on a topic that no page
    links to, unless it is listed as menu-only (account) - and on a
    stale exception.

Known until the change that follows: the dns, dmarc and account topics
describe the three-choice report address, which the code does not have
yet; Account's DMARC box still links to #dns.

Not verified by running: three sentences rest on Postfix behaviour
(delivery is deferred when a required TLS session cannot be made; a
milter with default_action=tempfail answers 4xx; with "any recipient"
an address the upstream refuses comes back as a bounce).

Evidence
  - docs/assets/panel-redesign/evidence/help.png (1440x3600) and
    in-domain.png: headless Edge, real templates served locally with
    their fixtures - NOT from the container.
  - go test -count=1 ./internal/web/... ./cmd/panel: ok (six packages).

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

CHANGELOG.md

@@ -113,6 +113,10 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); version
   the help drawer is gone. The user form sets the user's e-mail. The backup
   download is encrypted unless the box is unticked. Only the queue page is
   left on the ratchet.
+- panel-redesign (design, stage 3): **Help** covers every section -
+  seventeen topics for Overview, Outbound, Inbound, Server and Account - and
+  the boxes of nearly every page carry a `?` that opens their topic (owner,
+  2026-10-10). A reader sees the topics of the sections their menu shows.
 - panel-redesign (stage 2): the **Outbound queue** page is in the new shell
   with its content unchanged - the listing of `postqueue -p` and how
   retries work. With it every page is built from the component kit: the old