Studio: Ensure that the blueprint cards are proportionate in the blueprints gallery (#4156)

## Related issues

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Fixes STU-1853

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It was used to make a change, although it was pretty straightforward. 

## Proposed Changes

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This PR ensures that the blueprint cards are proportionate on the
blueprints gallery page. `height: 100%` makes every card stretch to the
tallest card in its grid row.

**Before**

<img width="792" height="241" alt="Screenshot 2026-07-10 at 9 46 58 AM"
src="https://github.com/user-attachments/assets/d99bd502-c041-47c1-bd76-0198f194fc5e"
/>

**After**

<img width="1038" height="317" alt="Screenshot 2026-07-10 at 9 47 19 AM"
src="https://github.com/user-attachments/assets/e6db9833-37e5-47da-9a49-9333099663b5"
/>

## Testing Instructions

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* Pull the changes from this branch
* Start Studio with `npm start`
* Enable the `Agentic UI` feature flag from `Studio -> Feature flags`
from the topbar
* Click on the `New site ->  Start from a blueprint` option
* Scroll through the blueprints gallery and confirm that you can see the
same height for each card

## Pre-merge Checklist

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- [ ] Have you checked for TypeScript, React or other console errors?

Co-authored-by: Kateryna Kodonenko <kateryna@automattic.com>

Author: katinthehatsite

apps/ui/src/components/blueprint-selector/style.module.css

@@ -47,6 +47,7 @@
 	display: flex;
 	flex-direction: column;
 	width: 100%;
+	height: 100%;
 	padding: 0;
 	border: 1px solid var(--wpds-color-stroke-surface-neutral, #ddd);
 	border-radius: 8px;