Refine optional helper approval experience

[bigboateng]

Summary

This follows PR #66 and closes the remaining optional-helper developer experience gaps.

• Use one ordered installer operation plan for both preview and execution.
• Show resolved paths, dependency preparation, workflow verification, agent registration, and final adapter verification before confirmation.
• Ask Apply this helper install plan? [y/N].
• Render summary, primitives, exact files, and exact commands before every builder mutation in TypeScript, Python, Go, and Rust.
• Clarify that conversion source_path is the source skill directory, not its SKILL.md file.
• Document Python helper installation through the installed module launcher.

The manual workflow remains the primary onboarding path. Package installation still creates no helper skill or adapter; developers must explicitly install the optional helper and restart their coding agent.

Safety and compatibility

• Keeps yskill bootstrap and npm create @operatorstack/yield compatible.
• Keeps skills/yield-workflow-builder as the canonical helper.
• Preserves dry-run, cancellation, ownership, path escape, existing destination, repair-limit, and version guards.
• Declined mutations leave tracked files unchanged.
• Adds no command or flag.

Verification

Passed locally:

• npm run format:check
• go test ./cmd/yskill
• go test ./...
• go build ./...
• npm run test:release (46 tests)
• Python SDK unit tests
• Rust SDK tests
• TypeScript SDK tests and build
• Cross-runtime builder compilation and seven-mode fixtures

A disposable first-run journey confirmed that the full approval plan is visible and a decline leaves the tracked index and diff byte-for-byte unchanged. The approved conversion generated a workflow that passed doctor --test, Codex registration, and adapter verification.

The exact-version helper verification inside that journey reached the two-repair fail-closed boundary because the package candidate was intentionally unpublished and unavailable to the generated pinned uvx launcher. This does not affect a matching published package and is why public documentation remains gated on release.