final review polish: clear remaining stale markers

- TIMELINE 2019/2020: replaced empty '(pending)' lines with explicit
  notes that no concept files trace to those years (refinements were
  folded into adjacent year entries).
- TIMELINE 2025: stripped stale '(pending)' from FOMC two-stage and
  Advanced Liquidity entries (both Phase 7 files have shipped).
- INDEX 99-glossary section: replaced '(Phase 8)' placeholder with
  explanatory note pointing to root GLOSSARY.md and the 10
  inline disambiguation files. References 99-glossary/README.md.

All audit checks still pass:
  - 226 concept files validated (10 sections, JSON parse, id-match)
  - 0 broken cross-links
  - 0 orphan source citations
  - INDEX.md and TIMELINE.md fully aligned with disk
  - Only remaining (pending) marker is the GLOSSARY explanatory header