docs: clarify OpenCode V2 beta release flow

[CasualDeveloper]

Summary

Follow-up to the non-blocking observations in the PR #33 review.

• Document that each OpenCode V2 beta release requires a reviewed X.Y.Z-beta.N version bump before dispatching the workflow.
• Clarify that the release workflow publishes the exact reviewed version and never creates version commits.
• Explain why the constants regression test intentionally launches a fresh Bun process through process.execPath.

The permissive numeric forms accepted by Number() remain unchanged because strict decimal-only configuration is not currently required.

Verification

• npm run verify
• V1 smoke suite passes.
• 40 V2/shared tests pass.
• Typecheck, build, package validation, and OpenCode V2 loader smoke pass.
• Release workflow YAML parses successfully.

Refs #31.