posthog-integration publishes the wrong skill under skills/all

Fix in #308.

posthog-integration currently ships omnibus-instrument-product-analytics under skills/all. The SDK-integration omnibus (omnibus-instrument-integration) is absent from the published plugin entirely — anyone installing the plugin gets the wrong skill and never receives the integration one.

Reproduce

Live, no clone needed:

gh api repos/PostHog/skills/contents/skills/posthog/integration/skills/all/SKILL.md \
  --jq '.content' | base64 -d | grep '^name:'

name: omnibus-instrument-product-analytics     # expected: omnibus-instrument-integration

Locally, the count mismatch is the tell:

pnpm build | grep 'posthog-integration'                          # ✓ posthog-integration (40 skills)
ls dist/marketplace/plugins/posthog-integration/skills | wc -l   # 39

Cause

shortId is a skill's variant id within its group (skill-generator.js:315-329), so it is unique only per-group. A plugin aggregates many groups, so marketplace-generator.js:181 puts a group-scoped key into a plugin-scoped namespace.

omnibus/instrument-integration and omnibus/instrument-product-analytics both declare category: integration with a single variant id: all, so both resolve to plugins/posthog-integration/skills/all.

The mega-plugin at :200 already keys by skill.id and is unaffected.

It is not a clean overwrite

copyDirSync (:50-61) does mkdirSync + copyFileSync with no clearing, so it merges file-by-file. The survivor keeps the loser's files that it does not itself have. The published all/ is a hybrid: product-analytics' SKILL.md over 8 orphan integration references — js.md, node.md, react.md, posthog-js.md, posthog-node.md, EXAMPLE-javascript-web.md, EXAMPLE-javascript-node.md, EXAMPLE-react-vite.md. All 8 are in the published tree today:

gh api repos/PostHog/skills/contents/skills/posthog/integration/skills/all/references \
  --jq '.[].name' | grep -E '^(js|node|react|posthog-js|posthog-node)\.md$'

Why it stayed silent

The build logs ✓ posthog-integration (40 skills) from the input count while writing 39 dirs, and marketplace-generator.js has no test coverage.

Only posthog-integration is affected — every other plugin's dir count already matches its log line.

Start in marketplace-generator.js around lines 181 and 200, then read skill-generator.js around lines 315-329 and copyDirSync around lines 50-61. Run pnpm build and inspect the generated posthog-integration directory and counts. Done means the integration and product-analytics skills publish separately, with no hybrid directory or count mismatch.