fix(examples-py): validate Chroma, Hugging Face, and Instructor OTel 2.x spans

[Nightingalelyy]

Summary

• propagate the exact shared marker through Chroma examples
• add a real local Hugging Face pipeline with an in-memory tokenizer and tiny randomly initialized GPT-2 model
• make Instructor examples use the Respan facade, repository gateway credentials, bounded workflow content, explicit shutdown, and a complete runner
• remove the stale legacy Instructor example that bypassed the documented gateway setup

Validation

• all 5 Chroma examples passed against editable local packages
• all 4 Hugging Face examples passed, including the real local pipeline and privacy case
• all 5 Instructor sync/async examples passed through the Respan gateway
• exact marker otel2-fix-py-group-15-20260817T084907Z returned 14 traces and 52 full records
• every tree and record was inspected through Respan MCP for hierarchy, content, types, tokens, tools, errors, grouping, and duplicates
• Python compilation, Black formatting, Ruff import/static checks, and git diff checks passed