feat: add MiniMax as first-class LLM provider

[octo-patch]

Summary

Add MiniMax as the 7th LLM provider in RuoYi AI, following the existing factory pattern.

Changes

• ChatModeType enum: Add MINIMAX("minimax", "MiniMax") enum value
• MinimaxServiceImpl: Chat provider using OpenAiStreamingChatModel with MiniMax OpenAI-compatible API (https://api.minimax.io/v1), supports streaming and thinking mode
• MinimaxEmbeddingProvider: Embedding provider extending OpenAiEmbeddingProvider for MiniMax embo-01 model (1536 dimensions)
• SQL migration: Provider registration and default model entries (M2.7, M2.5, M2.5-highspeed chat models + embo-01 embedding model)
• README/README_EN: Add MiniMax to the supported providers list

Supported Models

Model	Category	Context Window
MiniMax-M2.7	Chat	1M tokens
MiniMax-M2.5	Chat	204K tokens
MiniMax-M2.5-highspeed	Chat	204K tokens
embo-01	Embedding	1536 dims

Architecture

Follows the same pattern as existing providers (DeepSeek, PPIO):

• Implements AbstractChatService interface
• Auto-discovered by ChatServiceFactory via Spring @Service
• Uses LangChain4j OpenAiStreamingChatModel for OpenAI-compatible API

Test Plan

• 14 unit tests (MinimaxServiceImplTest: 5, MinimaxEmbeddingProviderTest: 4, ChatModeTypeTest: 5)
• 3 integration tests (MinimaxIntegrationTest, requires MINIMAX_API_KEY)
• All 17 tests pass
• Full project compiles successfully with mvn compile

[ageerle]

感谢贡献！MiniMax provider 已通过手动合并到 main 分支（提交 081da6d），合并时解决了冲突并补充了 MyChatModelListener 监听，与其他 provider 保持一致。此 PR 可以关闭了。