feat: automatic proxy re-sync on settings change

When domain, SSL certificate, or proxy provider changes in settings:
- Delete old proxy routes from the previous provider
- Switch to None: clear all route IDs on instances
- Switch to NPM/Traefik: re-create routes with new settings
- Domain change: re-configure all routes with new FQDN
- SSL cert change: re-apply to all existing routes
- Provider created dynamically at runtime via createProxyProvider()
- Deployer and API server updated via SetProxyProvider callback

internal/deployer/deployer.go

@@ -67,6 +67,11 @@ func New(
 	}
 }
 
+// SetProxyProvider updates the proxy provider at runtime (e.g., when settings change).
+func (d *Deployer) SetProxyProvider(provider proxy.Provider) {
+	d.proxy = provider
+}
+
 // SetDNSProvider sets the DNS provider for managing DNS records during deployments.
 // Pass nil to disable DNS management (wildcard DNS mode).
 func (d *Deployer) SetDNSProvider(provider dns.Provider) {