refactor(cli): improve error handling for remote script fetch

[apoorvdarshan]

Ref #1394

// Before: process.exit(1) — abrupt, no error propagation
// After: throws Fail with descriptive message
await $`npx zx http://example.com/nonexistent.mjs`
// stderr: Error: Can't get http://...
//         Failed to fetch remote script: http://... (404)

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[antongolub]

We'd like to avoid bloating comments, so the current try-catches are fine. But the explicit error related to fetch seems reasonable. I would only support this change.

[apoorvdarshan]

@antongolub Thanks for the feedback! Scoped the PR to only the fetch error handling change in readScriptFromHttp — removed all the catch block comments.

[antongolub]

Follow the PR template hints:

1. update bundles
2. add/update autotests

[apoorvdarshan]

@antongolub Updated — bundle rebuilt and added assertions to the existing scripts from https 500 test to verify the new Fail error message and exit code. Also updated the PR description to follow the template.

[apoorvdarshan]

@antongolub Squashed everything into a single clean commit rebased on latest main. Only the fetch error handling change remains — no catch block comments. Bundle and test updated.