feat: add MiniMax provider support (#1406)

Add MiniMax as a new AI model provider with OpenAI-compatible API.

Supported models:
- MiniMax-M2.5 (default) - Peak Performance, Ultimate Value
- MiniMax-M2.5-highspeed - Same performance, faster and more agile

Changes:
- Add MiniMax client (mcp/minimax_client.go) with OpenAI-compatible API
- Add comprehensive unit tests (mcp/minimax_client_test.go)
- Add WithMiniMaxConfig option (mcp/options.go)
- Register MiniMax provider in trader, debate engine, backtest, and API
- Add MiniMax to frontend provider config and model icons
- Add MiniMax SVG icon

API Base URL: https://api.minimax.io/v1

mcp/minimax_client.go

@@ -0,0 +1,83 @@
+package mcp
+
+import (
+	"net/http"
+)
+
+const (
+	ProviderMiniMax       = "minimax"
+	DefaultMiniMaxBaseURL = "https://api.minimax.io/v1"
+	DefaultMiniMaxModel   = "MiniMax-M2.5"
+)
+
+type MiniMaxClient struct {
+	*Client
+}
+
+// NewMiniMaxClient creates MiniMax client (backward compatible)
+func NewMiniMaxClient() AIClient {
+	return NewMiniMaxClientWithOptions()
+}
+
+// NewMiniMaxClientWithOptions creates MiniMax client (supports options pattern)
+//
+// Usage examples:
+//
+//	// Basic usage
+//	client := mcp.NewMiniMaxClientWithOptions()
+//
+//	// Custom configuration
+//	client := mcp.NewMiniMaxClientWithOptions(
+//	    mcp.WithAPIKey("sk-xxx"),
+//	    mcp.WithLogger(customLogger),
+//	    mcp.WithTimeout(60*time.Second),
+//	)
+func NewMiniMaxClientWithOptions(opts ...ClientOption) AIClient {
+	// 1. Create MiniMax preset options
+	minimaxOpts := []ClientOption{
+		WithProvider(ProviderMiniMax),
+		WithModel(DefaultMiniMaxModel),
+		WithBaseURL(DefaultMiniMaxBaseURL),
+	}
+
+	// 2. Merge user options (user options have higher priority)
+	allOpts := append(minimaxOpts, opts...)
+
+	// 3. Create base client
+	baseClient := NewClient(allOpts...).(*Client)
+
+	// 4. Create MiniMax client
+	minimaxClient := &MiniMaxClient{
+		Client: baseClient,
+	}
+
+	// 5. Set hooks to point to MiniMaxClient (implement dynamic dispatch)
+	baseClient.hooks = minimaxClient
+
+	return minimaxClient
+}
+
+func (c *MiniMaxClient) SetAPIKey(apiKey string, customURL string, customModel string) {
+	c.APIKey = apiKey
+
+	if len(apiKey) > 8 {
+		c.logger.Infof("🔧 [MCP] MiniMax API Key: %s...%s", apiKey[:4], apiKey[len(apiKey)-4:])
+	}
+	if customURL != "" {
+		c.BaseURL = customURL
+		c.logger.Infof("🔧 [MCP] MiniMax using custom BaseURL: %s", customURL)
+	} else {
+		c.logger.Infof("🔧 [MCP] MiniMax using default BaseURL: %s", c.BaseURL)
+	}
+	if customModel != "" {
+		c.Model = customModel
+		c.logger.Infof("🔧 [MCP] MiniMax using custom Model: %s", customModel)
+	} else {
+		c.logger.Infof("🔧 [MCP] MiniMax using default Model: %s", c.Model)
+	}
+}
+
+// MiniMax uses standard OpenAI-compatible API with Bearer auth
+func (c *MiniMaxClient) setAuthHeader(reqHeaders http.Header) {
+	c.Client.setAuthHeader(reqHeaders)
+}