Refresh base-demo AI context for representative environment

[codeforester]

Summary

• refresh .ai-context/manifest.md so it describes the committed representative environment instead of future work
• document the current service catalog, Compose infrastructure, multi-language fixtures, React/Vite console, service dry-run contract, and expanded build targets
• add a validation guard so the stale future-tense AI-context wording does not return
• pin the base-bash-libs CI checkout to the same Base v1.5.0-compatible SHA used by Base CI

Root Cause

base-demo grew into the representative environment, but the manifest AI-context note still described services, infrastructure, UI, and environment modeling as future work.

While validating the PR, the macOS GitHub Actions job also exposed a sibling dependency drift: base-demo pinned Base to v1.5.0, but left base-bash-libs floating on main. Current base-bash-libs main no longer matches Base v1.5.0's setup expectations, so the workflow now pins that checkout as well.

Closes #162.

Validation

• ./tests/validate.sh
• git diff --check
• /Users/rameshhp/work/base/bin/basectl export-context --format markdown --print