Narrow the canonical workspace manifest to the Base ecosystem

[codeforester]

Goal

Keep the canonical base-workspace manifest focused on Base source development and first-party validation.

Background

The manifest currently mixes Base repositories with personal projects and adjacent integration repositories. That makes basectl workspace update, clone planning, and workspace readiness reports operate on repositories that are not required to develop Base. Marking unrelated repositories optional would not fully solve the problem because present optional repositories are still updated.

Scope

• Keep these required repositories: base, base-bash-libs, base-cli, and base-workspace.
• Keep these first-party validation repositories as optional: base-demo, base-cli-demo, and base-bash-libs-demo.
• Remove bankbuddy, brew, blend, and bleach from the canonical manifest.
• Remove the adjacent but non-core base-platform-tools and banyanlabs repositories from the canonical manifest.
• Add validation coverage for the exact canonical membership and required/optional classification.
• Update README/changelog wording to explain the boundary.

Acceptance criteria

• The manifest contains exactly the four required Base repositories and three optional first-party demo repositories listed above.
• Personal projects and adjacent integration repositories are absent from the canonical manifest.
• Repository validation fails if a removed repository is reintroduced or a core/demo classification changes unexpectedly.
• A Base workspace clone dry run plans only the four required repositories and skips missing optional demos.
• No local checkout is deleted or moved by this change.
• No separate personal or integration manifest is introduced in this PR; that can be added later if needed.

Validation

• ./tests/validate.sh
• git diff --check
• Base workspace clone dry run using an empty temporary workspace

Project fields

• Status: In Progress
• Priority: P2
• Area: Workspace
• Initiative: Adoption Polish
• Size: S

Agent assignment

Implementation and validation are assigned to the coding agent. Keep the change limited to the canonical manifest and its repository-owned validation/documentation.