feat: add web gateway hot reload and polling state sync (#1684)

* feat(gateway): support hot reload and empty startup

- extract gateway runtime into pkg/gateway
- add gateway.hot_reload config with default and example values
- allow starting the gateway without a default model via --allow-empty
- stop treating missing enabled channels as a startup error
- update related tests

* feat: replace gateway SSE updates with polling-based state sync

- remove gateway SSE broadcasting and event endpoint
- add polling-based gateway status refresh with stopping state handling
- detect when gateway restart is required after default model changes
- resolve gateway health and websocket proxy targets from configured host
- update gateway UI labels and add backend/frontend test coverage

pkg/config/config.go

@@ -625,8 +625,9 @@ func (c *ModelConfig) Validate() error {
 }
 
 type GatewayConfig struct {
-	Host string `json:"host" env:"PICOCLAW_GATEWAY_HOST"`
-	Port int    `json:"port" env:"PICOCLAW_GATEWAY_PORT"`
+	Host      string `json:"host"       env:"PICOCLAW_GATEWAY_HOST"`
+	Port      int    `json:"port"       env:"PICOCLAW_GATEWAY_PORT"`
+	HotReload bool   `json:"hot_reload" env:"PICOCLAW_GATEWAY_HOT_RELOAD"`
 }
 
 type ToolDiscoveryConfig struct {

pkg/config/config_test.go

@@ -267,6 +267,9 @@ func TestDefaultConfig_Gateway(t *testing.T) {
 	if cfg.Gateway.Port == 0 {
 		t.Error("Gateway port should have default value")
 	}
+	if cfg.Gateway.HotReload {
+		t.Error("Gateway hot reload should be disabled by default")
+	}
 }
 
 // TestDefaultConfig_Providers verifies provider structure

pkg/config/defaults.go

@@ -395,8 +395,9 @@ func DefaultConfig() *Config {
 			},
 		},
 		Gateway: GatewayConfig{
-			Host: "127.0.0.1",
-			Port: 18790,
+			Host:      "127.0.0.1",
+			Port:      18790,
+			HotReload: false,
 		},
 		Tools: ToolsConfig{
 			MediaCleanup: MediaCleanupConfig{