panel-redesign: Inbound domains, domain and delete on the kit; Spam filter box

Stage 2, step 5. Written by Sonnet, reviewed by Opus.

  - Three pages named after their mockups: in-domains, in-domain,
    in-domain-delete, with typed page data (view/inbound.go), fixtures
    and tests. The engine pages inbound, inbound_domain and
    inbound_delete are gone with their templates and are off
    legacy_pages.txt.
  - The Spam filter box (plan, Who sees what). The panel now reads
    INBOUND_ANTISPAM_MILTER and INBOUND_ANTISPAM_MILTER_ACTION, with the
    semantics of build/postfix-config.sh (on only with the inbound relay
    on and a milter set; accept | tempfail). It reports them, nothing
    more:
      on   Applies to / Filter (the address, global role only) / If the
           filter is down (accepted unfiltered | deferred)
      off  one sentence; the variable is named for the global role only
    The list shows "Spam filter on|off" in its head.
  - Handlers pass typed data; routes, POST targets, field names,
    validation and authorization (global: all inbound domains; domain
    role: the assigned ones, another tenant's id is a 404; add and
    delete are global-only) are unchanged. A test saves the upstream and
    recipients forms untouched and finds the domain unchanged.

Left out of the mockups' Spam filter box and menu - no source before
inbound-antispam-panel (2.1): the engine name, the quarantine row, the
"refused at the door, see the log" row, the lists row, "Log for this
domain". Also "Checked N min ago" on the MX box: the check carries no
time.

Not done: the filter's socket on Health and Overview. internal/health
checks a unix socket by stat; the documented form of the filter's
address is inet:host:port and needs a dial that does not exist yet.

Differences from the mockups, for the owner:
  - refusals and confirmations are the kit flash above the boxes;
  - the MX tag is coloured by the check in every state; an MX that
    points elsewhere shows "In DNS now";
  - the lead of the domain page follows what is saved ("Not accepting
    mail yet: no upstream is saved");
  - the delete page lists only what the domain has;
  - /help#inbound opens Help at the top until the Help step.

Evidence
  - docs/assets/panel-redesign/evidence/in-domains.png, in-domain.png,
    in-domain-delete.png: 1440 px wide, headless Edge, real templates
    served locally with their fixtures (filter on) - NOT from the
    container (no Docker on this machine).
  - panel/audit.js on the three pages at 1440 and 1280: 352 texts
    checked, problems: [].
  - That the panel process sees the two variables inside the container
    is read from supervisord.conf and entrypoint.sh, not run.
  - go test -count=1 ./internal/web/... ./cmd/panel
      ok  internal/web
      ok  internal/web/auth
      ok  internal/web/handlers
      ok  internal/web/validate
      ok  internal/web/view
      ok  cmd/panel

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

internal/web/view/view.go

@@ -52,9 +52,9 @@ var pageFiles = map[string][]string{
 	"out-app":             {"templates/out_app.html"},
 	"out-app-created":     {"templates/out_app_created.html"},
 	"out-domain-delete":   {"templates/out_domain_delete.html"},
-	"inbound":             {"templates/inbound.html"},
-	"inbound_domain":      {"templates/inbound_domain.html"},
-	"inbound_delete":      {"templates/inbound_delete.html"},
+	"in-domains":          {"templates/in_domains.html"},
+	"in-domain":           {"templates/in_domain.html"},
+	"in-domain-delete":    {"templates/in_domain_delete.html"},
 	"out-log":             {"templates/out_log.html", "templates/out_log_rows.html"},
 	"out-message":         {"templates/out_message.html"},
 	"dmarc":               {"templates/dmarc.html"},
@@ -88,6 +88,10 @@ var kitPages = map[string]bool{
 	"out-app-created":     true,
 	"out-domain-delete":   true,
 
+	"in-domains":       true,
+	"in-domain":        true,
+	"in-domain-delete": true,
+
 	"out-log":      true,
 	"out-message":  true,
 	"dmarc":        true,