add APIs for getting toolbox items

[Mahmoud1205]

fixes #190
there are two new APIs: GetCategories which returns a list of categories with their names and IDs.
and GetItems which returns a list of items from a category ID. or all the categories if a category ID wasn't selected
the API is very simple but i will upgrade it soon if this PR gets merged.

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[whatbeato]

hey, thanks for the pr! before this can be merged there are a few things that need to be fixed though:

the category IDs aren't stable - you're using the array index as the ID, so if anyone reorders the manifest the IDs shift and GetItems starts returning the wrong data. there's no actual ID field on manifest entries so this whole concept is a bit fragile.

GetItems has inconsistent response shapes - if you don't pass a category, it returns { categories: manifest } (the whole manifest), but if you do pass one, it returns the full category object including color, icon, etc. instead of just the items. the endpoint is called GetItems so it should probably just return items. the two cases should return the same shape.

file naming - Next.js API routes are conventionally lowercase or kebab-case, not PascalCase. GetCategories.js -> get-categories.js, etc.

the yarn.lock diff is huge (+360/-695) - can you explain what changed there? dependency changes need to be intentional, not a side effect of running install with a different node version.

brace style is inconsistent between the two files. pick one and stick to it.

great work, but it just needs a bit of cleanup before it's ready to merge! i've marked it as a draft for now :)