v0.16.0

• Plain --brief no longer discards a paid distillation: rebuilding
  the free skeleton onto the stamped brief file now grafts the existing
  distilled section (with freshness notes re-derived) and carries the
  distillation stamp forward — same behavior the SessionEnd refresh
  always had. An explicit -o elsewhere still writes a plain skeleton.
• Git-aware freshness: the brief now knows the repo, not just the
  session store. The skeleton carries a Repo HEAD line (short hash +
  date + subject of the last commit); the SessionEnd refresh and the
  SessionStart injection warn when commits landed after the last
  distillation ("N commit(s) newer than this memory"), so outdated
  memory is never trusted silently. Read straight from
  .git/logs/HEAD — no git subprocess, keeping the
  deterministic-mode invariant; silently absent outside a repo.
• Brief layout fix: the LLM-distilled sections (Decisions / Fixed /
  Conventions / Open threads) now render as ### sub-headings nested
  under ## Distilled memory instead of rivaling it. Demoted
  deterministically at assembly — prompts unchanged, so every cached
  session note survives.