feat(PROJ-22): LDAP Web-GUI + feat(PROJ-21): Multi-Tenancy Phase 1

PROJ-22 – LDAP Web-GUI Konfiguration & Test:
- internal/ldapconfig/store.go: AES-256-GCM Passwortspeicherung, CRUD Upsert (id=1)
- internal/ldapauth/client.go: TestConnection (RootDSE, UserCount) + Authenticate (2-step bind)
- internal/auth/auth.go: LDAP-Fallback in Login(), Gruppen-Rollenzuordnung, issueToken helper
- internal/api/ldap_tenants.go: GET/PUT/DELETE/POST-test /api/admin/ldap mit Audit-Log
- go.mod: github.com/go-ldap/ldap/v3 v3.4.8 hinzugefügt
- Frontend: LDAPConfig/LDAPTestResult Typen, LDAP-Tab mit Gruppen-Mappings + Testergebnis

PROJ-21 Phase 1+6+7 – Multi-Tenancy Grundstruktur:
- internal/tenantstore/store.go: tenants, tenant_domains, tenant_ldap Schema; Migration users/audit_log
- API: 8 Tenant-Routen (CRUD + Domain-Management) via SetTenants()
- cmd/archivmail/main.go: ldapSt + tenantSt initialisiert
- Frontend: Mandanten-Tab mit Tabelle, Domain-Dialog, Deaktivieren/Löschen

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/api/server.go

@@ -22,9 +22,11 @@ import (
 	"github.com/archivmail/internal/auth"
 	imapstore "github.com/archivmail/internal/imap"
 	"github.com/archivmail/internal/index"
+	ldapcfg "github.com/archivmail/internal/ldapconfig"
 	pop3store "github.com/archivmail/internal/pop3"
 	"github.com/archivmail/internal/smtpd"
 	"github.com/archivmail/internal/storage"
+	"github.com/archivmail/internal/tenantstore"
 	"github.com/archivmail/internal/userstore"
 	"github.com/archivmail/pkg/mailparser"
 )
@@ -50,6 +52,8 @@ type Server struct {
 	pop3Store     *pop3store.Store
 	pop3Importer  *pop3store.Importer
 	uploadJobs    sync.Map // jobID → *UploadJob
+	ldapStore     *ldapcfg.Store
+	tenantStore   *tenantstore.Store
 }
 
 // SetSMTPDaemon wires the SMTP daemon into the API server after construction.