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>

internal/web/view/overview.go

@@ -69,7 +69,7 @@ func NewOverview(m Meta, host string, cards []HealthCard, updated time.Time, day
 		Head:  overviewHead(host, cards, updated),
 		Health: Box{No: "01", Title: "Server health", ID: "health", Poll: "/overview/fragment",
 			End:  Rich(Link("/server/health", "All details")),
-			Help: &HelpLink{Href: "/help#checks", Title: "What these checks mean"}},
+			Help: topicLink(HelpChecks, "What these checks mean")},
 		Outbound: Box{No: "02", Title: "Outbound domains", End: Rich(Link("/outbound/domains", "Manage"))},
 		OutboundEmpty: EmptyState{Icon: "ti-world-upload",
 			Text: Plain("No outbound domains yet. Add the first one under Outbound.")},