Write config.json after a hot apply (#6686)

* Write config.json after a hot apply

tryHotApply only updated the in-memory snapshot, so bin/config.json stayed
stale until the next cold start and the Telegram/Discord config backups
uploaded old rules. Persist the new config once the API calls succeed; a
write failure is logged and does not restart the running core.

* Test that a hot apply refreshes config.json

internal/xray/process.go

@@ -316,6 +316,22 @@ func (p *Process) SetConfig(config *Config) {
 	p.config = config
 }
 
+// PersistConfig writes the current configuration snapshot to the config file,
+// keeping it in step after a hot apply (Start only writes it on a cold start).
+func (p *Process) PersistConfig() error {
+	p.mu.RLock()
+	data, err := json.MarshalIndent(p.config, "", "  ")
+	path := p.configPath
+	p.mu.RUnlock()
+	if err != nil {
+		return common.NewErrorf("Failed to generate XRAY configuration files: %v", err)
+	}
+	if path == "" {
+		path = GetConfigPath()
+	}
+	return writeFileAtomic(path, data, 0o600)
+}
+
 // GetOnlineClients returns the union of locally-online clients and
 // node-online clients from every registered remote panel. Dedupes by
 // email so a client connected to both a local and a node-managed inbound