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/handlers/handlers_help.go

@@ -6,13 +6,13 @@ import (
 	"github.com/mixeme/selfpost/internal/web/view"
 )
 
-// HandleHelp renders the Help page. It is for both roles; the topics about the
-// checks of Overview and Health are left out for a viewer who cannot see them.
+// HandleHelp renders the Help page. It is for both roles; the sections of pages
+// a viewer cannot open (Overview and Server, Inbound without a reach or with the
+// feature off, Outbound without a reach) are left out, as is their menu.
 func (h *Handlers) HandleHelp(w http.ResponseWriter, r *http.Request) {
-	p, ok := h.principal(r)
-	if !ok {
+	if _, ok := h.principal(r); !ok {
 		http.Error(w, "internal error", http.StatusInternalServerError)
 		return
 	}
-	h.view.Render(w, http.StatusOK, "help", view.NewHelp(h.shellMeta(r), p.IsGlobal()))
+	h.view.Render(w, http.StatusOK, "help", view.NewHelp(h.shellMeta(r), h.cfg.InboundEnabled))
 }