feat: rebuild TS LLM demos and rename package to scoped identity

[rlippmann]

Summary

• rebuild TypeScript demos as real LLM-backed comparative demos aligned to Python demo flow and checkers
• add shared demos stack (llm_client.ts, common.ts, run_demo.ts) and env-driven fail-fast behavior
• add demos smoke coverage for runnable artifacts and runner markers
• rename package to @rlippmann/context-compiler and update install/import docs
• validate build/test/pack and install-from-tarball runtime for demos

Notes

• repo name remains context-compiler-ts; package identity is now scoped for publish
• demo outcomes may vary by provider/client/serving path (noted in demos README)

Verification

• npm run build
• npm test
• npm pack
• install tarball in temp project and run import plus demo scripts