fix: serve JavaScript assets with a stable MIME type

[LeoGrosjean]

Summary

• serve .js and .mjs static assets as text/javascript rather than relying on host MIME mappings
• cover identity and precompressed responses when the system reports .js as text/plain

Problem

On Windows, Python reads the .js content type from the registry. If it is registered as text/plain, production Reflex serves ES-module assets with that type, and browsers reject them before the frontend can hydrate.

Testing

• uv run ruff check reflex/utils/precompressed_staticfiles.py tests/units/utils/test_precompressed_staticfiles.py
• uv run pytest tests/units/utils/test_precompressed_staticfiles.py

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[greptile-apps]

Greptile Summary

The PR stabilizes the MIME type used for JavaScript static assets so host-specific MIME mappings cannot prevent frontend hydration.

• Forces .js and .mjs identity and precompressed responses to use text/javascript.
• Adds unit coverage for identity and gzip responses when the system maps JavaScript to text/plain.
• Adds a bug-fix release note.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
reflex/utils/precompressed_staticfiles.py	Computes media types from the original asset path and explicitly normalizes JavaScript modules to text/javascript.
tests/units/utils/test_precompressed_staticfiles.py	Verifies stable JavaScript MIME handling for identity and gzip responses under an incorrect host MIME mapping.
news/6831.bugfix.md	Documents the Windows frontend hydration fix.

_{Reviews (2): Last reviewed commit: "chore: add changelog fragment for JavaSc..." | Re-trigger Greptile}

[codspeed-hq]

Merging this PR will not alter performance

✅ 26 untouched benchmarks
⏩ 8 skipped benchmarks¹

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_{Comparing LeoGrosjean:fix/windows-js-mime (0404cb7) with main (a08a061)}

Footnotes

1. 8 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[cubic-dev-ai]

No issues found across 2 files

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[cubic-dev-ai]

No issues found across 3 files

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