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/store/store.go

@@ -8,6 +8,7 @@ package store
 import (
 	"database/sql"
 	"embed"
+	"errors"
 	"fmt"
 	"io/fs"
 	"sort"
@@ -50,6 +51,14 @@ func (s *Store) Close() error {
 	return s.db.Close()
 }
 
+// applicationID marks a database file as a 2.x SelfPost one ("SP20"). The
+// baseline migration sets it.
+const applicationID = 0x53503230
+
+// ErrForeignSchema is returned by Open for a database that has a schema but
+// was not created by SelfPost 2.x — in practice a 1.x data directory.
+var ErrForeignSchema = errors.New("database was not created by SelfPost 2.x; 2.0 starts from an empty data directory (docs/schema-migrations.md)")
+
 // migrate applies embedded migrations in filename order, tracking progress via
 // SQLite's PRAGMA user_version so each migration runs at most once.
 func (s *Store) migrate() error {
@@ -70,6 +79,23 @@ func (s *Store) migrate() error {
 		return fmt.Errorf("read schema version: %w", err)
 	}
 
+	// A 1.x file carries a user_version from the deleted 1.x chain. Counting it
+	// against today's files would skip the baseline and leave the panel running
+	// on a schema it does not know, so such a file is refused outright; nothing
+	// is migrated from 1.x (docs/schema-migrations.md).
+	if version > 0 {
+		var appID int64
+		if err := s.db.QueryRow("PRAGMA application_id").Scan(&appID); err != nil {
+			return fmt.Errorf("read application id: %w", err)
+		}
+		if appID != applicationID {
+			return fmt.Errorf("schema version %d: %w", version, ErrForeignSchema)
+		}
+	}
+	if version > len(names) {
+		return fmt.Errorf("database schema version %d is newer than this build knows (%d)", version, len(names))
+	}
+
 	for i, name := range names {
 		target := i + 1
 		if target <= version {