panel-redesign: the 2.0 schema from zero - one baseline, no 1.x chain

Stage 1, step 1. BREAKING: a 1.x database is not migrated.

Schema
  - internal/store/migrations/ holds one file, 0001_init.sql, equal to the
    2.0 schema; 0002..0010 are deleted (they stay in history at 1.9.5). No
    admin table created and dropped, no ALTERs.
  - users.email replaces users.dmarc_report_email: the address is the
    user's own. The default DMARC report address is a user's setting
    (dmarc_default_mode hosted/account/custom/none, dmarc_default_address);
    the instance setting that mirrored the global user's field is gone.
  - domains.dmarc_rua_user_id: a domain follows a named user's default, or
    has an address of its own in dmarc_rua ('' = none). ON DELETE SET NULL
    leaves it at "no reports", never at someone else's default.
  - user_inbound_domains, users.all_domains, users.all_inbound_domains: in
    the schema for the inbound delegation of the next step.
  - users.role is 'global' / 'domain' (was 'domain_admin');
    rate_limits.allowed_ips, unused since 1.9.0, is dropped.

Opening a database
  - The baseline sets PRAGMA application_id ("SP20"). store.Open refuses a
    file that has a schema version without it (ErrForeignSchema) and one
    newer than the build. A 1.x file at user_version 10 would otherwise read
    as already migrated. The refused file is left untouched.

Code
  - Store.DomainDMARCRua is the one place a domain's report address is
    resolved; dnscheck.ResolveDMARCRua and Store.GlobalDMARCReportEmail are
    gone. dmarc.AllowedRecipients, the domain page, the dashboard and the
    DNS re-check go through it.
  - The old templates keep working on the new model until their pages are
    restyled: the Settings form's address field is the account e-mail and
    switches the user's default between it and none; a domain's "Same as
    Settings" makes it follow the user who chose it; a new or imported
    domain follows its creator.
  - Domain export/import: a domain that follows a user exports no address.

Tests: the baseline pinned table by table (TestBaselineSchema), refusal of a
1.x and of a newer database, constraints and cascades of the new columns and
table, resolution in every default mode, the deleted-user case, and the three
bridged handlers.

docs/schema-migrations.md is rewritten for the baseline; roadmap 11/27,
schema-squash marked built.

go test ./...   (Windows)
  ok for every package except two that fail the same way before this commit:
  internal/domain  TestWriteLoadPrivateKeyRoundtrip (file mode on NTFS)
  internal/logtail TestFollowTailsAndRotates (rename of an open file)

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

internal/web/handlers/handlers_dmarc.go

@@ -1,7 +1,6 @@
 package handlers
 
 import (
-	"database/sql"
 	"fmt"
 	"net/http"
 	"strings"
@@ -26,12 +25,14 @@ func (h *Handlers) HandleDomainDMARC(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	var rua sql.NullString
+	// "inherit" makes the domain follow the default of the user who chose it;
+	// every other mode gives the domain an address of its own ("" = none).
+	follow := false
+	rua := ""
 	switch strings.TrimSpace(r.PostFormValue("dmarc_rua_mode")) {
 	case "inherit":
-		rua = sql.NullString{}
+		follow = true
 	case "none":
-		rua = sql.NullString{Valid: true, String: ""}
 	case "custom":
 		email := strings.TrimSpace(r.PostFormValue("dmarc_rua_email"))
 		if err := validate.Email(email); err != nil {
@@ -42,20 +43,25 @@ func (h *Handlers) HandleDomainDMARC(w http.ResponseWriter, r *http.Request) {
 			h.renderDomainDetail(w, r, http.StatusBadRequest, d, detailView{FormErr: "Enter a custom report address or choose another mode."})
 			return
 		}
-		rua = sql.NullString{Valid: true, String: email}
+		rua = email
 	case "hosted":
 		if h.dmarc == nil || !h.dmarc.Enabled() {
 			h.renderDomainDetail(w, r, http.StatusBadRequest, d, detailView{FormErr: "SelfPost-hosted reports are not enabled on this server."})
 			return
 		}
-		addr := dmarc.HostedReportAddress(h.cfg.Hostname, d.Name)
-		rua = sql.NullString{Valid: true, String: addr}
+		rua = dmarc.HostedReportAddress(h.cfg.Hostname, d.Name)
 	default:
 		h.renderDomainDetail(w, r, http.StatusBadRequest, d, detailView{FormErr: "Choose how aggregate reports are addressed for this domain."})
 		return
 	}
 
-	if err := h.store.UpdateDomainDMARCRua(d.ID, rua); err != nil {
+	var err error
+	if p, ok := h.principal(r); follow && ok {
+		err = h.store.SetDomainDMARCUser(d.ID, p.ID)
+	} else {
+		err = h.store.SetDomainDMARCAddress(d.ID, rua)
+	}
+	if err != nil {
 		logf("panel: domain %d: save dmarc rua: %v", d.ID, err)
 		h.renderDomainDetail(w, r, http.StatusInternalServerError, d, detailView{FormErr: "Could not save DMARC settings. Please check the logs and try again."})
 		return