next.js

c505af99 - [skills] Mark insight-error-page and next-rspack as internal (#95070)

[skills] Mark insight-error-page and next-rspack as internal (#95070) These two maintainer skills live under `.agents/skills/` alongside the internal dev skills (`flags`, `create-pr`, `react-vendoring`, etc.), all of which carry `metadata.internal: true`. They were missing the flag, so the skill sync pulled them into the external/universal distribution. Adds `metadata.internal: true` to both, matching their siblings. <!-- NEXT_JS_LLM_PR -->