Expand demo walkthrough lifecycle coverage

[codeforester]

Summary

• Add a setup dry-run step that shows Brewfile, mise, manifest, and virtualenv reconciliation without mutating persistent setup state.
• Add basectl repo check . to distinguish repository baseline validation from project health.
• Re-run basectl check and basectl doctor after activation to demonstrate the post-activation green path.
• Add per-command narration, clearer command/output spacing, and a closing summary with next steps.
• Use process-local MISE_TRUSTED_CONFIG_PATHS for the walkthrough so mise checks can pass without changing persistent mise trust.

Validation

• bats tests/demo_test.bats
• ./tests/validate.sh
• env GRADLE_USER_HOME=/private/tmp/base-demo-gradle-89 bats tests/demo_test.bats tests/services_test.bats tests/environments_test.bats tests/infra_test.bats tests/go_api_test.bats tests/python_api_test.bats tests/java_services_test.bats tests/native_services_test.bats tests/demo_console_test.bats
• git diff --check

Notes

• Attempted the real ./demo/demo.sh --non-interactive with actual basectl, temp Base cache, and temp service state. It reached the new setup/check sections, but this machine has a pre-existing broken Base/project virtualenv after a Homebrew Python upgrade, so the real run remains blocked until the local venvs are recreated.

Fixes #92
Fixes #95