docs: update security section to reflect OS Keychain architecture

refactor(ig-yandex): migrate secrets from JSON file to OS Keychain via keyring

refactor(ig-transcribe): migrate secrets from JSON file to OS Keychain via keyring

refactor(todoist): migrate secrets from JSON file to OS Keychain via keyring

feat: add Yandex Cloud transcriber (restored from PR #1, refactored to project standards)

docs: finalize README by adding quiz and removing deferred skills

feat: add interactive_quiz skill

docs: add Zero-LLM-Contact security guidelines

docs: reorder skills by priority and remove frameworks reference

feat: add robust run.sh venv wrappers for API-heavy skills

refactor: restructure community skills to zero-LLM-contact standard

Merge PR #1: Add Instagram, YouTube, Todoist, and Zettelkasten rules

chore: remove obsolete concept_extractor skill

ADD

feat(skill): add serendipity engine (/spark) to generate novel connections from random notes