feat: configuration backup management with manual and auto backup

Add backup/restore functionality for the SQLite database. Users can
trigger manual backups, configure automatic backups on an interval
with retention policies, list/download/delete backups, and restore
from any backup.

- Backup engine using VACUUM INTO (safe with WAL mode)
- Backup metadata tracked in DB, files stored in DATA_DIR/backups/
- Settings: backup_enabled, backup_interval_hours, backup_retention_count
- API: POST/GET/DELETE /api/backups, download, restore endpoints
- Autobackup via cron scheduler with configurable interval
- Retention: prune on startup, after each backup (manual and auto)
- Orphan cleanup: removes backup files without metadata on startup
- Restore: replaces DB and triggers graceful server shutdown
- Settings UI: /settings/backup with toggle, interval, retention config
- Backup list with download, delete, restore actions
- i18n: English and Russian translations

internal/api/router.go

@@ -8,6 +8,7 @@ import (
 	"github.com/go-chi/chi/v5"
 
 	"github.com/alexei/docker-watcher/internal/auth"
+	"github.com/alexei/docker-watcher/internal/backup"
 	"github.com/alexei/docker-watcher/internal/crypto"
 	"github.com/alexei/docker-watcher/internal/dns"
 	"github.com/alexei/docker-watcher/internal/docker"
@@ -40,6 +41,10 @@ type Server struct {
 	dnsProviderMu        sync.RWMutex
 	dnsProvider          dns.Provider
 	onDNSProviderChanged DNSProviderChangedFunc
+
+	backupEngine *backup.Engine
+	dbPath       string
+	shutdownFunc func() // called after restore to trigger graceful shutdown
 }
 
 // NewServer creates a new API Server with all required dependencies.
@@ -86,6 +91,21 @@ func (s *Server) SetProxyManager(pm *proxy.Manager) {
 	s.proxyManager = pm
 }
 
+// SetBackupEngine sets the backup engine on the server.
+func (s *Server) SetBackupEngine(engine *backup.Engine) {
+	s.backupEngine = engine
+}
+
+// SetDBPath sets the database file path (needed for restore).
+func (s *Server) SetDBPath(path string) {
+	s.dbPath = path
+}
+
+// SetShutdownFunc sets the function called after a restore to trigger graceful shutdown.
+func (s *Server) SetShutdownFunc(fn func()) {
+	s.shutdownFunc = fn
+}
+
 // SetDNSProvider sets the current DNS provider on the server.
 func (s *Server) SetDNSProvider(provider dns.Provider) {
 	s.dnsProviderMu.Lock()
@@ -287,6 +307,13 @@ func (s *Server) Router() chi.Router {
 				r.Get("/dns/records", s.listDNSRecords)
 				r.Post("/dns/sync", s.syncDNSRecords)
 				r.Delete("/dns/records/{fqdn}", s.deleteDNSRecord)
+
+				// Backup endpoints.
+				r.Get("/backups", s.listBackups)
+				r.Post("/backups", s.triggerBackup)
+				r.Get("/backups/{id}/download", s.downloadBackup)
+				r.Delete("/backups/{id}", s.deleteBackup)
+				r.Post("/backups/{id}/restore", s.restoreBackup)
 			})
 		})
 	})