chore(core): format package

[opencode-agent]

Summary

• run the repository-pinned Prettier 3.6.2 across all files under packages/core
• normalize 86 previously unformatted source, test, script, and schema files

Checks

• bun x prettier --check packages/core
• bun typecheck from packages/core
• git diff --check
• bun x oxlint packages/core (passes with existing warnings, no errors)

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