Add MiniMax provider

[octo-patch]

Reason: MiniMax is not available as a first-class provider with dedicated credentials, regional endpoints, and current model metadata.

Changes

• Add a dedicated MiniMax HTTP provider with both supported API styles and global/China endpoint presets.
• Register MiniMax credentials, setup choices, default models, context, pricing, modalities, and thinking metadata.
• Add subscription-key redaction and focused provider tests.

Checks

• .venv/bin/python -m pytest -q (12 passed)
• .venv/bin/ruff check ifixai test_minimax_provider.py
• .venv/bin/ruff format --check ifixai/providers/minimax.py test_minimax_provider.py
• .venv/bin/mypy --follow-imports=skip ifixai/providers/minimax.py ifixai/cli/model_catalog.py
• .venv/bin/bandit -r ifixai -ll
• .venv/bin/ifixai validate plus every example fixture
• .venv/bin/mypy ifixai remains non-clean at the repository level (223 errors across 63 files); the changed modules pass the targeted typecheck above.

[stefyi-4355]

Two things I'd like sorted before this goes in.

First, the secret scrubbing only covers part of the surface. sk-cp- is the Coding Plan prefix, but standard platform keys are JWTs and don't match any of the patterns, which means looks_like_secret returns False and a key could end up written into a scorecard. Can you confirm which key shapes MiniMax actually issues and add the missing pattern?

Second, the M3 pricing in minimax.py is the wrong tier. MiniMax charges 0.30/1.20/0.06 up to 512k and 0.60/2.40/0.12 above it, but only the higher tier is hardcoded, so setup shows people double the real price for normal prompts.

A few smaller things for afterwards: coverage is at 62% with send_message and the whole error-mapping path untested; there's no anthropic-version header on the Messages path, which is worth a live smoke test since this is our first hand-rolled client; the judge tiebreaker and provider table in docs/testing-your-agent.md weren't updated; and the try/except ImportError in resolver.py can never fire because model_catalog and setup_cmd import the module unconditionally anyway.

[octo-patch]

Thanks for the review. I added JWT key detection and redaction, represented both MiniMax-M3 pricing tiers in setup, added the Messages compatibility header, updated the judge and provider docs, simplified the resolver import, and expanded request and error-path tests. I ran the full test suite (25 passed), focused MiniMax coverage (91%), ruff, mypy, bandit, and fixture validation.

[stefyi-4355]

lgtm