feat: upgrade default MiniMax model to M3

[Hansen1018]

Summary

• Problem: Upgrade default MiniMax model to the new M3 flagship tier
• What changed: Updated default MiniMax model from M2.7/M2.5 to M3 across all provider configs, added MiniMax-M3 to pricing at $0.20/call
• What did NOT change (scope boundary): All other AI models and providers remain unchanged. Older MiniMax model versions still available via custom model field.

M3 Model Specifications (per official docs)

• Architecture: MiniMax Sparse Attention (MSA)
• Context window: up to 1M tokens (at least 512K guaranteed usable)
• Modalities: Native multimodal — image and video input, can operate computer desktop
• Coding: Exceeds GPT-5.5 on SWE-Bench Pro
• Agent (BrowseComp): 83.5 score (vs Opus 4.7: 79.3)

Reference: https://minimaxi.com/M3 (released 2026-06-01)

Change Type

• Feature

Scope

• MCP / AI clients
• API / server
• Web UI / frontend

Testing

• go build ./... passes
• npm run build passes (web)
• go test ./... passes

Compatibility

• Backward compatible? (Yes - older MiniMax model versions still selectable via custom model field)
• Migration needed? (No)
• Config/env changes? (No)

[github-actions]

🤖 Advisory Check Results

These are advisory checks to help improve code quality. They won't block your PR from being merged.

📋 PR Information

Title Format: ✅ Good - Follows Conventional Commits
PR Size: 🟢 Small (13 lines: +7 -6)

🔧 Backend Checks

Go Formatting: ⚠️ Needs formatting

Files needing formatting

agent/execution_state.go
agent/model_provider_catalog.go
agent/skill_dag_runtime.go
agent/stock.go
api/errors.go
api/handler_wallet.go
cmd/e2e_builder_fee/main.go
kernel/formatter.go
kernel/grid_engine.go
kernel/validate_test.go

Go Vet: ✅ Good
Tests: ✅ Passed

Fix locally:

go fmt ./...      # Format code
go vet ./...      # Check for issues
go test ./...     # Run tests

⚛️ Frontend Checks

Build & Type Check: ✅ Success

Fix locally:

cd web
npm run build  # Test build (includes type checking)

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📖 Resources

• Contributing Guidelines
• Migration Guide

Questions? Feel free to ask in the comments! 🙏

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