[codex] Constrain dev setup to Base project

[codeforester]

Summary

Clarifies and enforces the basectl setup --dev boundary: Base developer dependencies are only valid for the Base project.

What Changed

• Resolves the setup project name from base_manifest.yaml when no positional project argument is provided.
• Keeps normal project setup ergonomic: basectl setup from a project checkout can still use the manifest project name.
• Fails cleanly when --dev is used for any project other than base, without emitting a fatal stack trace.
• Allows explicit Base setup from any checkout: basectl setup base --dev now uses $BASE_HOME/base_manifest.yaml instead of discovering the current repo's manifest.
• Moves developer dependency installation until after Base's Python bootstrap packages are available and the --dev project boundary has been validated.
• Runs the Python project setup layer through Base's bootstrap virtual environment while exporting BASE_PROJECT=<project> for artifact reconciliation.
• Updates BATS coverage for explicit project forwarding, omitted-project manifest inference, Base manifest forwarding, and the non-Base --dev failure path.

Why

--dev currently means "install Base developer/test tooling" such as BATS and GitHub CLI. It should not apply to downstream projects like brew. From /Users/rameshhp/work/brew, basectl setup --dev should produce a normal usage error. But basectl setup base --dev is explicit Base setup, so it should not accidentally read brew/base_manifest.yaml just because that is the current working directory.

Impact

• basectl setup from a Base-compatible project checkout can still infer the project from base_manifest.yaml.
• basectl setup --dev is allowed only for base.
• basectl setup --dev from brew exits 1 with a clean ERROR: message before installing BATS/gh or running project artifact setup.
• basectl setup base --dev from brew targets Base's own manifest and completes as Base setup.

Validation

• bats cli/bash/commands/basectl/tests/setup.bats passed all 42 tests.
• Verified from /Users/rameshhp/work/brew that /Users/rameshhp/work/base/bin/basectl setup --dev exits with: ERROR: --dev is only supported for the Base project. Run without --dev for project 'brew'.
• Verified from /Users/rameshhp/work/brew that /Users/rameshhp/work/base/bin/basectl setup base --dev reads /Users/rameshhp/work/base/base_manifest.yaml and completes successfully.