feat: support the Alpha release phase

[RafaelGSS]

feat: support the Alpha release phase

Node.js 27 introduces Alpha releases versioned as
vN.0.0-alpha.X.Y.Z (see nodejs/node#63135).

- Keep Alpha versions in the release data instead of letting nodevu
  coerce them into vN.0.0, and give them the new Alpha status.
- Add a /download/alpha page and warn that Alpha releases are not
  meant for production.
- Fall back to the latest LTS on /download/current and
  /download/archive/current while there is no Current release.
- Match pre-releases in the platform and installer checks.

Refs: https://github.com/nodejs/Release/issues/1187

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Project	Deployment	Actions	Updated
nodejs-org	Ready	Preview	Oct 16, 2026 8:48pm UTC

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.28%. Comparing base (7c40136) to head (37dec44).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9223      +/-   ##
==========================================
+ Coverage   86.13%   86.28%   +0.14%     
==========================================
  Files          86       86              
  Lines        6075     6139      +64     
  Branches      360      370      +10     
==========================================
+ Hits         5233     5297      +64     
  Misses        838      838              
  Partials        4        4              

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[github-actions]

📦 Build Size Comparison

Summary

Metric	Value
Old Total First Load JS	7.20 MB
New Total First Load JS	7.20 MB
Delta	5.32 KB (+0.07%)

Changes

🔄 Modified Routes (4)

Route	Old First Load JS	New First Load JS	Delta
/[locale]	1.69 MB	1.69 MB	📈 1.33 KB (+0.08%)
/[locale]/[...path]	1.69 MB	1.69 MB	📈 1.33 KB (+0.08%)
/[locale]/blog/[...path]	1.69 MB	1.69 MB	📈 1.33 KB (+0.08%)
/[locale]/download/archive/[version]	1.69 MB	1.69 MB	📈 1.33 KB (+0.08%)