fix(temporal): remove broken workflow runtime export

[gregkonush]

Summary

• Removes the published ./workflow/runtime subpath that points to a source and build output that do not exist.
• Adds a packaging-manifest regression that verifies every dist/src/*.js export is backed by a source module.
• Prevents consumers from resolving an advertised Temporal SDK entrypoint that can never load.

Related Issues

Addresses historical Codex review: #1845 (comment)

Testing

• bun test packages/temporal-bun-sdk/tests/packaging/manifest-packaging.test.ts — 12 passed.
• tsc --noEmit --project packages/temporal-bun-sdk/tsconfig.json --pretty false — passed.
• Oxfmt and git diff --check on changed files — passed.

Breaking Changes

Removes the nonfunctional @proompteng/temporal-bun-sdk/workflow/runtime export. No working consumer could load this subpath because neither its source module nor its published build output existed.

Checklist

• Testing section documents the exact validation performed.
• Screenshots are not applicable; Breaking Changes is filled in.
• The packaging regression documents and enforces the corrected public surface.