feat(ENG-258): Audit state machine with plan-mode gate and DRY fixes

[alnoki]

Changes

1. Add resume and resolve phases to the /audit skill: resume
   skips to pending findings when .audit/findings.md exists,
   resolve iterates the checklist and marks items as fixed
2. Add plan-mode gate to audit output so findings are presented
   for user approval before any edits are made
3. Add draft-to-ready step to /pr-title-description skill so
   updating a draft PR also marks it ready for review
4. Add .audit/ to .gitignore
5. Rename InputBufferHeader in interface/src/market.rs to
   RegisterMarketInputBuffer to eliminate duplicate struct name
   with memory::InputBufferHeader
6. Fix typo in docs/src/index.md ("want to more" -> "want more")

[linear]

ENG-258