Blueprints Gallery Library: Add search option to Blueprints

[katinthehatsite]

Related issues

Fixes STU-1634

How AI was used in this PR

It was used to implement the feature.

Proposed Changes

This PR adds a search box for the blueprints that allows search by excerpt or title:

Testing Instructions

• Pull the changes from this branch
• Start the app with npm start
• Enable the Blueprints Gallery Library feature flag
• Click on Add site > Build new site
• Scroll down to the blueprints library
• Confirm that you can use the search box and search by title or category

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[wpmobilebot]

📊 Performance Test Results

Comparing 16d5a30 vs trunk

app-size

Metric	trunk	16d5a30	Diff	Change
App Size (Mac)	1410.38 MB	1409.86 MB	0.52 MB	⚪ 0.0%

site-editor

Metric	trunk	16d5a30	Diff	Change
load	1501 ms	1491 ms	10 ms	⚪ 0.0%

site-startup

Metric	trunk	16d5a30	Diff	Change
siteCreation	8077 ms	8079 ms	+2 ms	⚪ 0.0%
siteStartup	4922 ms	4942 ms	+20 ms	⚪ 0.0%

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Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)