fix custom assetFileNames issue

[apatel369]

Changes

closes #426 in adapters repo

When using custom assetFileNames in Astro configuration assets were incorrectly moved to the server directory instead of the client directory. This caused 404 errors when the browser tried to load these assets from the client side.

Users could specify custom directories for various asset types (e.g., CSS, images). To handle that used asset paths from the build output to ensure assets are moved from/to the correct directories.

Testing

Added tests for testing image and CSS assets with custom paths.
The previous test was passing cause accidentally build.assets and custom assetFileNames path were matching.
(assets and assets/css)
So updated that as well.

Docs

N/A bug fix

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Latest commit: b07ac29

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[codspeed-hq]

CodSpeed Performance Report

Merging #12449 will improve performances by 42.54%

_{Comparing apatel369:arpan-#426-adp-customfilename (63ab7d9) with main (92c269b)}

Summary

⚡ 1 improvements
✅ 5 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	apatel369:arpan-#426-adp-customfilename	Change
⚡	Rendering: streaming [false], .mdx file	1,046.6 ms	734.2 ms	+42.54%