Circuit brief file rules

• *.brief.json follows the DesignBrief schema in src/circuit/brief.py
  and *.intake.json follows Intake/IntakeReport in
  src/circuit/intake.py; check the contract summary in
  plugins/circuit/skills/circuit-brief/SKILL.md before editing.
• Every claim in the matching *.intake.json binds to a provenance source:
  R* user-stated requirement, A* assumption with rationale, Q* open
  question, I* imported source. Details read off images are observations —
  A* or Q* with an evidence ref (kind, path, sha256, note),
  never R*.
• Generated artifacts (schematics, netlists, ERC/DRC reports, renders,
  exports, design report) are never hand-edited — change the brief and
  re-run the deterministic pipeline; gates stay fail-closed.