docs(architecture): align Studio docs with current boundaries

[ShuhaoZhangTony]

Summary

• replace the historical monorepo/chat-oriented README with the current visual workflow editor boundary
• document the real FastAPI entry point, CLI surface, project layout, installation, and validation commands
• remove references to deleted modules, missing scripts, and the old organization location
• update contributor/Copilot guidance and run CI for documentation-only pull requests
• add regression tests for removed runtime paths, broken local links, and the backend entry point

Validation

• python3 -m pytest -q tests/test_docs_consistency.py tests/test_boundary_dependency_audit.py tests/test_runtime_cleanup_guardrails.py
• ruff check tests/test_docs_consistency.py
• ruff format --check tests/test_docs_consistency.py
• result: 14 passed; lint and format checks passed

Closes #30.