feat: add MiniMax as a model provider

[octo-patch]

Summary

Add MiniMax as a first-class model provider in nexent, following the established provider pattern.

What is MiniMax?

MiniMax is a leading AI company offering powerful LLM and embedding models:

• MiniMax-M2.7: Latest flagship model with 1M token context window
• MiniMax-M2.5 / M2.5-highspeed: 204K context window, optimized for speed
• embo-01: Embedding model with 1536 dimensions

All models are accessible via an OpenAI-compatible API at https://api.minimax.io/v1.

Changes

Backend (5 files):

• backend/services/providers/minimax_provider.py — New MiniMaxModelProvider with model type classification (LLM, embedding, TTS, STT, reranker, VLM) and known context window sizes
• backend/consts/provider.py — Add MINIMAX enum, base URL, and models endpoint
• backend/services/providers/__init__.py — Export MiniMaxModelProvider
• backend/services/model_provider_service.py — Wire MiniMax into factory
• backend/services/model_management_service.py — Add MiniMax base URL for batch create

Frontend (5 files):

• frontend/hooks/model/useMinimaxModelList.ts — Batch import hook (follows DashScope pattern)
• frontend/app/[locale]/models/components/model/ModelAddDialog.tsx — Add MiniMax to provider dropdown
• frontend/const/modelConfig.ts — Provider constants (icon, hint, link)
• frontend/public/locales/{en,zh}/common.json — i18n translations
• frontend/public/minimax.png — Provider icon

Tests (1 file, 16 tests):

• test/backend/services/providers/test_minimax_provider.py — Unit tests covering all model types, known context windows, error handling (HTTP errors, connection errors, timeouts), authorization header, and mixed type classification

Test Plan

• All 16 new MiniMax provider unit tests pass
• All 102 existing provider tests continue to pass (118 total)
• Manual verification: batch import MiniMax models with API key
• Manual verification: MiniMax models appear in model list with correct types

[sonarqubecloud]

Quality Gate failed

Failed conditions
30.3% Duplication on New Code (required ≤ 3%)
D Security Rating on New Code (required ≥ A)

See analysis details on SonarQube Cloud

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