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>

cmd/panel/antispam_test.go

@@ -0,0 +1,34 @@
+package main
+
+import "testing"
+
+// The panel reads the inbound filter's two variables with the semantics of
+// build/postfix-config.sh: the action is accept unless it says tempfail, and a
+// value the script would refuse is not guessed at.
+func TestAntispamActionMirrorsTheBuildScript(t *testing.T) {
+	for raw, want := range map[string]string{
+		"": "accept", "accept": "accept", "tempfail": "tempfail",
+		"reject": "", "Accept": "", "TEMPFAIL": "", " accept": "",
+	} {
+		if got := antispamAction(raw); got != want {
+			t.Errorf("antispamAction(%q) = %q, want %q", raw, got, want)
+		}
+	}
+}
+
+func TestLoadConfigReadsTheInboundFilter(t *testing.T) {
+	t.Setenv("INBOUND_RELAY_ENABLE", "true")
+	t.Setenv("INBOUND_ANTISPAM_MILTER", "inet:antispam:11332")
+	t.Setenv("INBOUND_ANTISPAM_MILTER_ACTION", "tempfail")
+	cfg := loadConfig()
+	if !cfg.inboundEnabled || cfg.inboundAntispamMilter != "inet:antispam:11332" || cfg.inboundAntispamAction != "tempfail" {
+		t.Errorf("config = %+v", cfg)
+	}
+
+	t.Setenv("INBOUND_ANTISPAM_MILTER", "")
+	t.Setenv("INBOUND_ANTISPAM_MILTER_ACTION", "")
+	cfg = loadConfig()
+	if cfg.inboundAntispamMilter != "" || cfg.inboundAntispamAction != "accept" {
+		t.Errorf("unset filter: milter %q, action %q", cfg.inboundAntispamMilter, cfg.inboundAntispamAction)
+	}
+}