chore: update webpack-dev-server to v6 and test against v5 and v6

[bjohansebas]

Summary

Updates the webpack-dev-server dev dependency to v6 and makes the test suite cover both v5 and v6, which are the versions the webpack-cli peer range allows (^5.0.0 || ^6.0.0).

• Snapshots for dev-server 6 are added next to the existing v5 ones. The snapshot resolver already supports this through the .snap.devServer<major>.webpack<major> extension, so no tooling change was needed. The only difference in the output is the help text for --server-type, since v6 drops spdy from the possible values.
• CI runs the matrix against dev-server-version: [5, latest], installing v5 with npm install ... --no-save --ignore-scripts for that job, following the same approach as chore: use plugin support #4791.
• webpack-dev-server v6 is ESM and exposes the server as its default export, while v5 exports it directly, so tsc failed with "This expression is not constructable". The CLI now resolves the constructor type from the default export when there is one, which type-checks against both versions. Runtime behavior is unchanged: the package was already loaded through (await import(pkg)).default.

What kind of change does this PR introduce?

chore, plus a types fix in webpack-cli.

Did you add tests for your changes?

No new tests, the existing test/help and test/serve suites now run against both dev-server versions with their own snapshots.

Does this PR introduce a breaking change?

No. The peer range already allowed v6, and the type change only affects how the constructor type is resolved.

If relevant, what needs to be documented once your changes are merged or what have you already documented?

SERVE-OPTIONS-v6.md will be generated by the scheduled "Update documentation" workflow, which derives the filename from the installed dev-server major.

Use of AI

Yes. I used Claude Code (Opus) to carry out the upgrade under my direction: the dependency bump, the type fix, the CI matrix and the snapshots. I verified the build and ran test/help against the new snapshots locally, and reviewed the final diff.

[changeset-bot]

🦋 Changeset detected

Latest commit: 946aeb0

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
webpack-cli	Patch

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[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	webpack-dev-server@​5.2.5 ⏵ 6.0.0	+1	+3		+2

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[github-actions]

This PR is packaged and the instant preview is available (946aeb0).

Install it locally:

• npm

npm i -D webpack-cli@https://pkg.pr.new/webpack-cli@946aeb0

• yarn

yarn add -D webpack-cli@https://pkg.pr.new/webpack-cli@946aeb0

• pnpm

pnpm add -D webpack-cli@https://pkg.pr.new/webpack-cli@946aeb0

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.34%. Comparing base (0cfc077) to head (946aeb0).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4834      +/-   ##
==========================================
+ Coverage   93.32%   93.34%   +0.02%     
==========================================
  Files          14       14              
  Lines        5466     5472       +6     
  Branches      793      793              
==========================================
+ Hits         5101     5108       +7     
+ Misses        363      362       -1     
  Partials        2        2              

Files with missing lines	Coverage Δ
packages/webpack-cli/src/webpack-cli.ts	96.78% <100.00%> (+0.03%)	⬆️

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