chore: remove builtin skills and document local skill provenance

[dirtybits]

Summary

• remove only the builtin/preloaded Hermes skills: hermes-agent and obsidian
• restore the three local Hermes Agent-created umbrella skills: github-workflows, software-development-workflows, and research-intelligence-workflows
• add explicit provenance/attribution sections to each retained umbrella skill
• mark retained umbrella skills in registry.json as local-hermes-agent-created with candidate-with-attribution

Provenance spike

No exact public web/GitHub/Hermes-repo match was found for the three umbrella skill names. hermes-agent and obsidian were confirmed as Hermes repo builtins and remain removed.

Test Plan

• npm run kb:format
• npm run validate
• git diff --check