Stop publishing the repo as a plugin marketplace, and refresh the run skill

Three small things.

Removed `.claude-plugin/marketplace.json`. It is the file `/plugin
marketplace add` reads, so without it this repo no longer offers itself as a
marketplace — which is the odd part of an Angular app carrying one. The
caveman plugin's own files stay, so it can be listed from a marketplace of its
own later; only the listing is gone.

That left four documents asserting an install path that no longer exists,
including a README section handing out `/plugin marketplace add` and
`/plugin install` commands that would now fail. All four now say what is
actually true. `.junie/plans/nasa-star-map.md` still describes the repo as
containing only a marketplace, and is left alone: it records what was here
before the app was written, and is not a claim about the present.

The run skill's numbers had drifted a release behind — 496 tests in 28 files
against a real 527 in 31, and a build timed at 9s that now takes 12. Measured
rather than guessed. The pinned Playwright version it names was correct.

It also gains the Pages build, which is not a plain `npm run build`: the base
href and the 404.html copy are both required for a project site, and the
artifact root is `dist/star-map/browser` rather than its parent. Plus the
matching gotcha, since a Pages build served at `/` looks broken in a way that
tells you nothing about whether it would work.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WaySiNst4HhDXBHnMy8p5G

skills/caveman/SKILL.md

@@ -15,12 +15,10 @@ exactly as-is.
 
 ## Scope
 
-This skill ships via this repo's plugin marketplace
-(`.claude-plugin/marketplace.json`). Installing with
-`/plugin install caveman@star-map` defaults to **user scope** — global,
-available in every project — instead of being tied to just one repo. Use
-`--scope project` or `--scope local` to narrow it; see the
-[README](../../README.md).
+This repo no longer publishes itself as a plugin marketplace, so there is
+currently no install path for this skill from here. Listing it from a
+marketplace elsewhere is what would make `/plugin install` work again; see
+the [README](../../README.md).
 
 ## Persistence