feat: support DSH Headless profiles

[Grivn]

Summary

• mount Mnemon Agent tools, runtime context, lifecycle guidance, and cwd-based workspace routing without Web-only services
• discover the Web workspace registry lazily so existing workbench routing remains stable
• define one-shot shutdown semantics for delayed review and document Web/Headless capability boundaries in English and Chinese
• add an isolated real Headless-profile verification using a local mock model

Verification

• pnpm run verify
• 206 tests passed, 1 Windows-only smoke test skipped
• deterministic double build passed
• real Headless profile activation exposed representative Mnemon tools
• package contents, publint, and type exports passed