Switch bootstrap flow to demo target

[SatyKrish]

Summary

• rename the non-prod bundle target and docs/CI commands from dev to demo
• move the Vector Search endpoint into foundation and materialize the index before agent registration
• rename bootstrap-dev.sh to bootstrap-demo.sh and update target defaults/agent choices

Validation

• DATABRICKS_BUNDLE_ENGINE=direct databricks bundle validate --strict -t demo --var "warehouse_id=20d3b28c396a087e"
• bash -n scripts/bootstrap-demo.sh
• .venv/bin/python -m py_compile agent/log_and_register.py agent/retrieval.py scripts/wait_for_kpis.py

Deployment notes

• Demo deploy progressed through foundation, pipeline, model registration, and Vector Search index readiness.
• Databricks Model Serving endpoint analyst-agent-demo remained stuck in Container creation pending during live validation; this appears to be service provisioning rather than bundle validation.