Add a concept to the graph

Each node is one YAML file in plugins/runpod/skills/runpod-usage/concepts/ (called concepts/ below). The format, kinds, relation types and writing style are defined in concepts/README.md. Read it before writing; this skill is the procedure, not the format.

Every file is public-facing. Everything in it must be safe to show a customer and backed by a public source. The validator enforces this.

1. Check it doesn't already exist

Search ids, names and aliases before creating anything:

grep -ril "<term>" plugins/runpod/skills/runpod-usage/concepts/
cd ontology/tools && pnpm build:sqlite && pnpm query concept "<term>"   # resolves names and aliases
pnpm query search "<term>"                                     # finds rules that mention it