docs(readme): simplify sdk install examples

[samzong]

Summary

• Simplify the README TypeScript SDK embed example to the minimal install call.
• Point full CLI flag and workflow wiring to the API docs instead of duplicating it in the README.
• Tighten vision wording around public GitHub bundles without presenting kitup as a package manager.

Scope Check

• Stays within the v0.1 bundled-skill installer boundary.
• Does not add marketplace, registry, remote install, script execution, GUI, MCP server, or agent runtime behavior.
• Updates golden cases for observable installer behavior changes. Not applicable; docs-only change.
• Regenerates host constants after spec/hosts.json changes. Not applicable; host spec was not changed.

Verification

• make check