da0c88e376
check-broken-links parses every .md under docs/ as MDX and can't parse the plain-
markdown plan (code/angle brackets), failing CI. These are engine design docs, not
user documentation, so relocate docs/superpowers/{plans,references} (plan,
findings, research, diagrams) to internal-packages/run-engine/design/ and fix the
internal path references. Also run oxfmt on runEngine.server.ts (missed after the
review fix wave), fixing code-quality.