Demo walkthrough skips basectl setup, basectl repo check, and basectl doctor green-path

[codeforester]

Context

The demo walkthrough (`demo/demo.sh`) and the README Quick Start both list `basectl setup`, `basectl repo check`, and `basectl doctor` as key Base lifecycle commands, but the walkthrough never runs them:

• `basectl setup` is entirely absent from `demo.sh`. A user watching the demo never sees Brewfile reconciliation or `mise` toolchain installation fire.
• `basectl repo check` appears in the README Quick Start but is not in the demo steps.
• `basectl doctor` appears only as a pre-activation diagnostic (expected to fail, Step 4). The demo never shows `doctor` passing after activation. A learner may conclude `doctor` is a failure-diagnosis tool only.

These three commands are among the most important Base lifecycle commands for a new user to see. Their absence from the walkthrough leaves a gap between the README description and the interactive experience.

Scope

• Add a Setup step to `demo.sh` that runs `basectl setup base-demo` (or shows expected output if setup is assumed complete) and explains what it reconciles.
• Add `basectl repo check .` to the project-shape or manifest step, so learners see repository-level baseline validation distinct from project-level check.
• After the activation step (Step 5), re-run `basectl check` and `basectl doctor` to show the green-path output and contrast with the pre-activation diagnostic.
• Update `tests/demo_test.bats` to cover the new steps.

Validation

• `./demo/demo.sh --non-interactive` completes without error and output includes the new step titles.
• `tests/demo_test.bats` covers setup, repo check, and post-activation doctor.
• `./tests/validate.sh`