v0.8.42 — every install gets the whole manifest, as real copies

Fixed

• Both skill-delivery paths now agree on what a symlink means, and neither
  skips the manifest. v0.8.41 made sync_skills.sh phase 1 manifest-driven;
  verifying the result on four real installs showed two of them had never
  received Documentation/schema.md at all, while the script reported
  success. Phase 2 short-circuited on scripts/ being a symlink and continued
  past everything else — so the symlink, which only makes memory_bridge.py
  auto-current, was being read as "this whole install is current".

  This is the second time that short-circuit has caused exactly this, and the
  first fix is why it recurred: SKILL.md was hoisted above the continue, a
  per-file repair to a per-loop defect, so the next file added to the
  manifest fell into the identical hole. Phase 2 now iterates MANIFEST.txt,
  and the short-circuit decides one thing only — whether update_skill.sh needs
  to run.

• update_skill.sh no longer writes through a symlink. It applied every
  staged file with mv, which replaces a symlink with a regular file. So the
  self-update path silently undid the arrangement the sync path depends on: a
  repo-linked file, auto-current by construction, became a frozen copy of that
  day's content — invisible until it had gone stale. The exact mirror of the
  defect above, on the other delivery path. A symlinked destination is now left
  as a link and reported as such.

Changed

• ⛔ An installed skill file is now always a REAL COPY, never a symlink into a
  source checkout. Repo-linking memory_bridge.py bought auto-currency at a
  price that is only visible once: it binds every agent on the machine to one
  checkout's path, so moving, renaming or archiving the project breaks all of
  them at once — silently, with the first symptom being an agent failing
  mid-task. Staleness is the lesser risk precisely because it is detectable:
  every file is content-compared on each sync and doctor reports version skew.
  It also makes the local development path produce the same result as the
  shipped one, since update_skill.sh fetches from GitHub and writes real files
  for everybody else already.

  Both delivery paths now replace any symlink they find, and both close the
  hazard that creates: cp and cmp each follow a link, so a naive
  implementation would write into the source tree and would report a link
  pointing at identical content as "already current" forever. A symlinked
  scripts/ or Documentation/ is dissolved into a real directory before
  anything is written inside it, and sync_skills.sh refuses an install
  directory that is itself a link rather than making the source its own
  destination. README's four per-agent blocks now copy the whole package —
  they previously installed two of the six files the manifest ships — and
  AGENTS.md states the copy-only rule.

• sync_skills.sh's agent list is env-overridable via
  SHARED_MEMORY_SYNC_AGENTS (colon-separated), instead of four $HOME paths
  baked into a code path. Those four are our agent set, not the agent set —
  and hardcoding them is also what made this delivery logic untestable, which is
  how the same defect shipped twice. tests/test_skill_delivery.py now runs the
  real scripts against a temporary tree and asserts what actually lands there,
  because the whole defect class lives in shell control flow: a test that read
  the source for a filename would have passed throughout both failures, since
  the filename was there — above a continue that skipped it.