feat(cloud): Add custom cloud API URL configuration support (#181)

* feat(cloud): Add custom cloud API URL configuration support

- Implement RPC methods to set, get, and reset cloud URL
- Update cloud registration to remove hardcoded cloud API URL
- Modify UI to allow configuring custom cloud API URL in developer settings
- Remove environment-specific cloud configuration files
- Simplify cloud URL configuration in UI config

* fix(ui): Update cloud app URL to production environment in device mode

* refactor(ui): Remove SIGNAL_API env & Rename to DEVICE_API to make clear distinction between  CLOUD_API and DEVICE_API.

* feat(ui): Only show Cloud API URL Change on device mode

* fix(cloud): Don't override the CloudURL on deregistration from the cloud.

cloud.go

@@ -96,7 +96,6 @@ func handleCloudRegister(c *gin.Context) {
 	}
 
 	config.CloudToken = tokenResp.SecretToken
-	config.CloudURL = req.CloudAPI
 
 	provider, err := oidc.NewProvider(c, "https://accounts.google.com")
 	if err != nil {
@@ -298,8 +297,8 @@ func rpcDeregisterDevice() error {
 	// (e.g., wrong cloud token, already deregistered). Regardless of the reason, we can safely remove it.
 	if resp.StatusCode == http.StatusNotFound || (resp.StatusCode >= 200 && resp.StatusCode < 300) {
 		config.CloudToken = ""
-		config.CloudURL = ""
 		config.GoogleIdentity = ""
+
 		if err := SaveConfig(); err != nil {
 			return fmt.Errorf("failed to save configuration after deregistering: %w", err)
 		}