0.5.2

Tooling and documentation only — nothing in the extension itself changed.

0.5.1 was tagged and never shipped: the manifest was left at 0.5.0, so the
release workflow's version guard refused it, which is precisely what that guard
is for.

Fixed

• The release workflow could not be re-run. It skips the Marketplace when
  VSCE_PAT is absent and tells you to add the secret and run it again — but
  gh release create fails outright once the release exists, so the advice was
  impossible to follow. An existing release is now updated in place.

• dist/preview/ no longer ships in the VSIX. It only exists once somebody has
  run vp run preview, so the extension gained 40 kB of developer artifact on
  some machines and not others.

• The README badges were dead. shields.io has retired its entire
  visual-studio-marketplace family — version, installs, downloads and rating
  all answer "retired badge". They are replaced by a static Marketplace link
  plus release, build and licence, none of which can rot.

  The obvious substitute, vsmarketplacebadges.dev, works and was rejected: the
  Marketplace renders images only from an allowlist of hosts, so those badges
  would have looked right on GitHub and broken on the listing itself. Losing
  version, installs and rating costs nothing there, since the Marketplace page
  already shows all three.

Changed

• Developer guidance moved from README.md to CONTRIBUTING.md. The README is
  the Marketplace listing, so build instructions and package layout were being
  shown to every prospective user.

Testing

• GitHub's rendering is now checked against GitHub's rendering. The Primer
  panel in vp run preview was a palette written from memory, which made the
  central claim of the colour design — that the semantic classes stay distinct
  where the palette is narrowest — one nobody could verify. It now runs the
  committed grammar through starry-night,
  the open reimplementation of GitHub's highlighter, coloured from the tokens
  @primer/primitives publishes.

  It found two things the approximation was hiding. markup.quote and
  entity.name.tag both resolve to pl-ent, so a citation and a name are the
  same colour on github.com; and variable.other resolves to pl-smi, whose
  colour is Primer's own foreground, so linkage tags are indistinguishable
  from ordinary text there. Six semantic classes come out as four colours in
  light and five in dark, not six. All of it is recorded in
  packages/grammar/test/prettylights.test.ts rather than assumed away.

  It also confirms the new payload-shape rules arrive as pl-ii, the class
  GitHub paints as invalid, rather than as ordinary text.