Studio: Allow hidden files import within wp-content

[katinthehatsite]

Related issues

Fixes https://linear.app/a8c/issue/STU-40/hidden-files-not-imported

Proposed Changes

This PR ensures that you can import hidden files into Studio (such as .gitignore) if they are located within wp-content folder.

Testing Instructions

• Pull the changes from this branch
• On Studio site A, add a hidden file to wp-content folder e.g. .gitignore
• Export site A through the Export option in the Export/Import tab
• Click on Add site
• Select Import from a backup
• Use the backup from site A
• Once the import is completed, open the new site in Finder and confirm that the hidden file is present in the wp-content directory

Pre-merge Checklist

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

[wpmobilebot]

📊 Performance Test Results

Comparing 4840158 vs trunk

site-editor

Metric	trunk	4840158	Diff	Change
load	1469.00 ms	1430.00 ms	-39.00 ms	⚪ 0.0%

site-startup

Metric	trunk	4840158	Diff	Change
siteCreation	7114.00 ms	8144.00 ms	+1030.00 ms	🔴 14.5%
siteStartup	4930.00 ms	4947.00 ms	+17.00 ms	⚪ 0.0%

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Results are median values from multiple test runs.

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