Release v0.2.1

[nightboy87]

Summary

Prepare the v0.2.1 staged release.

Added

• Add optional semantic cache support via skilltopo semantic-cache build.
• Add --semantic-cache support for recommend, workflow, and eval.
• Add semantic cache read/write/validation helpers and cached router usage.
• Add a synthetic Hermes-like integration example.
• Add documentation for semantic cold-start cost and model download behavior.
• Add Code of Conduct, issue templates, and pull request template.

Verification

Local verification completed before pushing this branch:

python -m pytest
# 17 passed

python -m skilltopo validate examples/skills --json
# valid: true, skill_count: 9

python -m skilltopo eval evals/skilltopo_50_seed.yaml --skills examples/skills --json
# 50/50 passed, accuracy_at_1: 1.0

Real semantic environment test was also performed in an isolated virtual environment and cleaned up afterward:

• sentence-transformers loaded successfully.
• skilltopo eval ... --semantic passed 50/50.
• Semantic cold-start behavior is documented.

Notes

• Keyword-first routing remains the default.
• Semantic matching remains optional.
• SkillTopo still does not execute skills or grant permissions.