fix(build): copy .astro content files to external outDir

[raman976]

Fixes #14903

Changes

• Fix content files not being copied when outDir is outside project directory
• Add copyDotAstroFiles() function to copy .astro/ files to external outDir
• Ensure content collections work consistently regardless of outDir location

Testing

• Added content-outdir-external.test.js to verify files are copied to external outDir
• Tested with mock scenarios to validate the fix resolves the reported issue
• No existing functionality affected

Docs

No docs needed - this is a bug fix that restores expected behavior without changing the API.

[changeset-bot]

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Latest commit: a36c36a

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[codspeed-hq]

CodSpeed Performance Report

Merging #14938 will not alter performance

_{Comparing raman976:main (a36c36a) with main (c8ac8e5)}

Summary

✅ 6 untouched

[Steffan153]

If I understand this correctly, isn't this the opposite of what the issue was? These files were being generated with an external outDir, but not with an outDir inside the project directory. I thought it was because the files were being cleaned up with a normal outDir, but with an external one they didn't get cleaned up.

[raman976]

Yeah ,I made a mistake in my first attempt at #14903. Totally misread it and was copying files when I should've been removing them. Fixed now in the latest commit! please review it