fix: Improve /sync with quality audit phase, consistent structure, and optional dependencies

- Add Phase 3: Quality Audit that checks existing rules against Claude Code
  best practices (size, specificity, redundancy, conflicts, path-scoping,
  skills candidates, stale references, emphasis gaps, CLAUDE.md overlap)
- Add Claude Code Best Practices Reference section in Phase 0 from official docs
- Restructure all phases sequentially (0-12) — remove fractional numbering
  (1.5, 1.7) and zero-indexed steps (4.0)
- Make Probe CLI optional with Grep/Glob/Read fallbacks throughout
- Make /learn skill optional with direct SKILL.md creation fallback
- Make Pilot-specific references generic (framework-provided servers, global
  user rules) so /sync works without Pilot Shell installed

Author: maxritter