Curate demo and product vision drafts into design docs

[codeforester]

Summary

Fold the useful design intent from the untracked draft documents into the existing Base design docs, then remove the drafts from local working context after review.

Drafts being curated locally:

• docs/base-demo-spec.md
• docs/product-vision.md

Scope

• Preserve the durable demo distinctions in the existing demo docs: Base self-demo vs. base-demo peer repo, reference implementation vs. interactive walkthrough, demo testing expectations, and the manual needs-demo maintenance model.
• Preserve the durable product direction in the existing architecture and boundary docs: Base as a Mac-first multi-repo workspace control plane, the product loop, adapter-first growth, doctor as a flagship capability, observability, adoption milestones, and team/workspace boundaries.
• Do not copy stale draft details verbatim. Update old terminology such as manifest.yaml, old demo script names, obsolete manifest fields, and over-specific generated automation ideas before integrating.
• Review whether each material design intent is already implemented or tracked by an open GitHub issue. Create follow-up issues for missing design intents.

Acceptance Criteria

• Existing design docs absorb the relevant draft content without adding duplicate standalone draft docs.
• The untracked draft files are left untouched for manual removal.
• Obsolete draft content is not promoted into canonical docs.
• Missing design intents are tracked as GitHub issues with clear scope and labels.

Validation

• Documentation diff review
• git diff --check