[opencode-go] Add reasoning options

[rekram1-node]

Summary

• backfill reasoning controls for every existing OpenCode Go model
• expose effective high|max effort levels for DeepSeek V4
• expose provider-supported MiMo effort controls
• mark MiniMax M3 as toggleable and fixed-reasoning models as having no user control
• preserve existing pricing and non-reasoning metadata

Validation

• bun validate
• git diff --check