Bundled update-config skill dumps full settings.json schema on every invocation

## Summary

The bundled `update-config` skill unconditionally returns its full settings.json JSON Schema reference — every field (sandbox config, marketplace source types, hook schemas, credential masking, etc.), several thousand lines — as part of its tool result on every single invocation, regardless of what the actual task needs.

## Measured impact

Invoking the skill for a trivial two-line `permissions.allow` edit consumed roughly 17.6% of that session's context window, almost entirely from the schema dump rather than any content relevant to the task.

## Suggestion

Make the schema reference something grep-searchable / looked up on demand (e.g. a reference file the skill can search or partially quote) instead of an unconditional full inline dump. That way trivial edits (adding a permission, setting an env var, etc.) don't pay the cost of loading the entire settings.json schema reference into context.

Start by locating the bundled update-config skill and the settings.json JSON Schema reference it returns. Trace how the skill assembles its tool result, then verify that a trivial permissions.allow or environment-variable edit no longer includes the full schema while schema details remain available on demand.

Written by the indexing model from the issue text.