Go: add balance command (#14262)

### What problem does this PR solve?

```
RAGFlow(user)> list supported models from 'moonshot' 'test';
+---------------------------------+
| model_name                      |
+---------------------------------+
| moonshot-v1-32k-vision-preview  |
| kimi-k2.6                       |
| moonshot-v1-8k                  |
| moonshot-v1-auto                |
| moonshot-v1-128k                |
| moonshot-v1-32k                 |
| kimi-k2.5                       |
| moonshot-v1-8k-vision-preview   |
| moonshot-v1-128k-vision-preview |
+---------------------------------+
RAGFlow(user)> show balance from 'moonshot' 'test';
+---------+----------+
| balance | currency |
+---------+----------+
| 0       | CNY      |
+---------+----------+
```

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

internal/cli/user_command.go

@@ -1234,6 +1234,47 @@ func (c *RAGFlowClient) ShowProviderInstance(cmd *Command) (ResponseIf, error) {
 	return &result, nil
 }
 
+// ShowInstanceBalance shows balance of a specific instance
+// SHOW BALANCE FROM PROVIDER <provider_name> <instance_name>
+func (c *RAGFlowClient) ShowInstanceBalance(cmd *Command) (ResponseIf, error) {
+	if c.ServerType != "user" {
+		return nil, fmt.Errorf("this command is only allowed in USER mode")
+	}
+
+	instanceName, ok := cmd.Params["instance_name"].(string)
+	if !ok {
+		return nil, fmt.Errorf("instance name not provided")
+	}
+
+	providerName, ok := cmd.Params["provider_name"].(string)
+	if !ok {
+		return nil, fmt.Errorf("provider name not provided")
+	}
+
+	url := fmt.Sprintf("/providers/%s/instances/%s/balance", providerName, instanceName)
+
+	resp, err := c.HTTPClient.Request("GET", url, true, "web", nil, nil)
+	if err != nil {
+		return nil, fmt.Errorf("failed to show instance: %w", err)
+	}
+
+	if resp.StatusCode != 200 {
+		return nil, fmt.Errorf("failed to show instance: HTTP %d, body: %s", resp.StatusCode, string(resp.Body))
+	}
+
+	var result CommonDataResponse
+	if err = json.Unmarshal(resp.Body, &result); err != nil {
+		return nil, fmt.Errorf("show instance failed: invalid JSON (%w)", err)
+	}
+
+	if result.Code != 0 {
+		return nil, fmt.Errorf("%s", result.Message)
+	}
+
+	result.Duration = resp.Duration
+	return &result, nil
+}
+
 // AlterProviderInstance renames a provider instance
 // ALTER INSTANCE <name> NAME <new_name> FROM PROVIDER <name>
 func (c *RAGFlowClient) AlterProviderInstance(cmd *Command) (ResponseIf, error) {