refactor: remove standalone proxies, add Traefik provider with Docker labels

Standalone proxy removal:
- Delete store, API handlers, proxy manager, health monitor, validator, hints
- Delete frontend pages (proxies list, create, edit) and components (ProxyCard, ProxyForm, ProxyFilter, ProxyGroup, ValidationChecklist)
- Remove proxy routes from router, nav items, dashboard references
- Clean up SystemHealthCard to remove proxy section

Traefik provider:
- Add TraefikProvider implementing proxy.Provider via Docker labels
- ContainerLabels() returns traefik.enable, router rule, entrypoints, service port, TLS cert resolver, docker network
- ConfigureRoute() returns router name (labels handle routing at container creation)
- DeleteRoute() is no-op (container removal auto-deregisters)
- Ping() checks Traefik API health (optional)
- Wire ContainerLabels into deployer (executeDeploy + blueGreenDeploy)
- Add Traefik settings: entrypoint, cert_resolver, network, api_url
- Add traefik option to proxy provider selector in settings UI
- Show conditional Traefik config fields
- Add i18n keys (EN + RU)

internal/store/models.go

@@ -63,8 +63,12 @@ type Settings struct {
 	DNSProvider          string `json:"dns_provider"`
 	CloudflareAPIToken   string `json:"cloudflare_api_token"`
 	CloudflareZoneID     string `json:"cloudflare_zone_id"`
-	ProxyProvider        string `json:"proxy_provider"`
-	BackupEnabled        bool   `json:"backup_enabled"`
+	ProxyProvider       string `json:"proxy_provider"`
+	TraefikEntrypoint   string `json:"traefik_entrypoint"`
+	TraefikCertResolver string `json:"traefik_cert_resolver"`
+	TraefikNetwork      string `json:"traefik_network"`
+	TraefikAPIURL       string `json:"traefik_api_url"`
+	BackupEnabled       bool   `json:"backup_enabled"`
 	BackupIntervalHours  int    `json:"backup_interval_hours"`
 	BackupRetentionCount int    `json:"backup_retention_count"`
 	UpdatedAt            string `json:"updated_at"`
@@ -194,16 +198,3 @@ type EventLog struct {
 	CreatedAt string `json:"created_at"`
 }
 
-// StandaloneProxy represents a standalone reverse proxy not tied to a project.
-type StandaloneProxy struct {
-	ID               string `json:"id"`
-	Domain           string `json:"domain"`
-	DestinationURL   string `json:"destination_url"`
-	DestinationPort  int    `json:"destination_port"`
-	SSLCertificateID int    `json:"ssl_certificate_id"`
-	NpmProxyID       int    `json:"npm_proxy_id"`
-	HealthStatus     string `json:"health_status"` // unknown, healthy, unhealthy
-	HealthCheckedAt  string `json:"health_checked_at"`
-	CreatedAt        string `json:"created_at"`
-	UpdatedAt        string `json:"updated_at"`
-}