feat: add MiniMax as first-class LLM provider (OpenAI-compat, M2.7, 204K context)

[octo-patch]

Summary

Finite Monkey Engine is an AI-driven smart-contract audit platform. All LLM calls currently flow through src/openai_api/openai.py using OPENAI_API_BASE / OPENAI_API_KEY environment variables, which makes it straightforward to plug in any OpenAI-compatible provider.

This PR adds first-class MiniMax support by introducing automatic provider detection and a temperature-clamping helper, so users can switch to MiniMax's high-context-window models without changing any other code.

Changes

File	What changed
src/openai_api/openai.py	_init_llm_config() auto-detects MiniMax; _clamp_temperature() enforces (0.01, 1.0]
env.example	New MINIMAX_API_KEY / LLM_PROVIDER section with model presets
README.md	"Using MiniMax as LLM Provider" section with quickstart table
tests/test_minimax_provider.py	20 unit tests
tests/integration/test_minimax_integration.py	7 integration tests

How it works

Auto-detection (zero config change for existing users):

# Option A: explicit
LLM_PROVIDER=minimax
MINIMAX_API_KEY=your-key

# Option B: just set the key — if OPENAI_API_KEY is absent, MiniMax is auto-selected
MINIMAX_API_KEY=your-key

_init_llm_config() runs at module import time and writes OPENAI_API_BASE=api.minimax.io + OPENAI_API_KEY=<minimax_key> into the process environment. Every existing helper (ask_openai_common, detect_vulnerabilities, etc.) then routes to MiniMax automatically — no other code changes needed.

Supported MiniMax models (all with 204 K context):

Model	Best for
MiniMax-M2.7	Flagship — vulnerability detection & reasoning
MiniMax-M2.7-highspeed	Fast JSON extraction & summarization
MiniMax-M2.5	Previous generation
MiniMax-M2.5-highspeed	Previous generation fast variant

Temperature safety: _clamp_temperature() enforces MiniMax's (0.0, 1.0] constraint (nudging 0 → 0.01) and is harmless for any other provider.

Testing

# Unit tests (20 tests)
python -m unittest discover -s tests -p "test_minimax_provider.py" -v

# Integration tests (7 tests)
python -m unittest discover -s tests/integration -p "test_minimax_integration.py" -v

All 27 tests pass.