fix(mcp): preserve category when loading component registry (#12694)

load_registry iterated data.values(), discarding the category
group keys from /api/v1/all. Every component ended up with
category: "", which made the components(category=...) MCP tool
filter return empty results for every category.

Iterate data.items() instead and inject the category name onto
each component's entry so search_registry's category filter works.