feat: add configurable plugin options

[ian-pascoe]

Summary

• Add Zod-backed plugin options for enablement, logging/toast behavior, tool metadata, and system guidance.
• Preserve current default behavior while allowing custom tool names/descriptions and prompt guidance.
• Document configuration and add a minor changeset.

Commits

• docs: add brv memories for plugin configuration keeps ByteRover memories isolated in a separate commit.
• feat: add configurable plugin options contains the package changes.

Verification

• pnpm test
• pnpm typecheck
• pnpm lint
• pnpm format:check
• pnpm build