feat: graceful degradation for cyclic schemas, code quality tightening

- Cyclic $ref left in place with $defs preserved (no throw)
- Non-cyclic refs still fully inlined
- Single-pass cycle tracking via cyclicDefs Set
- resolve() -> inlineRefs() with JSDoc
- Regex -> startsWith + slice
- Preserved $defs use cached resolved versions (fixes dangling $ref bug)
- Tests rewritten as declarative toEqual on full expected output
- Added multi-hop cycle test with shuffled $defs order
- ADR updated with review traceability and test philosophy

Author: gogakoreli