docs: deprecate the loader

[alexander-akait]

Summary

Marks the loader deprecated in the README and gives the migration in two forms: the one line where the file is yours (import { jQuery as $ } from "jquery"; globalThis.$ = $;), and the processResult plugin where it is not, linking to webpack's expose-global example (webpack/webpack#21952) as a working copy of it.

Neither form wraps the module in a second one, which is what the loader has to do — and what #25, #227 and #256 are about, so the README says which of them each form settles. It also notes the two things that decide whether the assignment runs: something has to import the module, and a file in a "sideEffects": false package needs { test: /…/, sideEffects: true }.

Documentation only — src/ is untouched, so the loader keeps working exactly as it does today.

Refs #25, refs #227, refs #256

What kind of change does this PR introduce?

docs

Did you add tests for your changes?

No — README only, no source change. npm test (68 tests) and npm run lint pass unchanged.

Does this PR introduce a breaking change?

No. The loader is unchanged; the deprecation is a notice, not a behavior change. npm deprecate and archiving remain separate decisions.

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

webpack.js.org's expose-loader page can carry the same notice and point at the example.

Use of AI

Written with Claude Code, reviewed and directed by me: the migration guide and the snippet were produced in that session, the snippet mirrors the merged example, and the claims about what the loader's wrapper module costs were checked against real builds before being written down.

🤖 Generated with Claude Code

https://claude.ai/code/session_01XWZM9YmKFi3ZeziHv69S4Q

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Generated by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.99%. Comparing base (5be92d7) to head (8130f2c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #277   +/-   ##
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  Coverage   72.99%   72.99%           
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  Files           4        4           
  Lines         137      137           
  Branches       51       51           
=======================================
  Hits          100      100           
  Misses         24       24           
  Partials       13       13           

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