fix: add Pioneer Ministral 3B route

[opencode-agent]

Summary

• add shared metadata for Ministral 3B
• add Pioneer's currently served ministral-3b route
• record Pioneer pricing and served output limit

Evidence

• Pioneer's public model API lists the route as active
• the API reports a 128,000-token input limit, 4,000-token output limit, and $0.10/$0.10 per million input/output tokens
• Mistral's launch documentation establishes the shared model identity and capabilities

Validation

• bun validate
• bun packages/core/script/sync-models.ts pioneer --dry-run --no-issues (0 updates; route no longer reported missing)

Closes #4133

Requested by: @rekram1-node (Aiden via Slack)

[github-actions]

No actionable findings.