fix(minimax): apply complete pricing tiers and modalities

[octo-patch]

Summary

• select all MiniMax-M3 pricing tiers from complete prompt size and request service tier
• retain cache token counts and the effective service tier for per-request cost calculation
• mark MiniMax-M2.7 as text-only in model capabilities

Verification

• uv run --frozen --extra dev --python 3.11 pytest -q tests/test_pricing_status_bar.py tests/test_model_system.py tests/test_minimax_provider.py tests/test_minimax_abort_signal.py tests/test_provider_registry.py tests/test_cost_tracker.py tests/test_cost_tracker_facade.py tests/test_cost_tracker_full.py tests/test_session_cost_persistence.py tests/server/test_cost_snapshot.py (164 passed)
• uvx ruff check --ignore F401,F541 src/services/pricing.py src/providers/minimax_provider.py src/models/configs.py tests/test_pricing_status_bar.py tests/test_model_system.py tests/test_minimax_provider.py
• request capture verifies both regional SDK base URLs, the appended /v1/messages path, and priority request metadata

Follow-up to #696.

[github-actions]

Test Results

    1 files      1 suites   8m 29s ⏱️
8 601 tests 8 595 ✅ 6 💤 0 ❌
8 786 runs  8 780 ✅ 6 💤 0 ❌

Results for commit 6b4a8af.

[agentforce314]

LGTM