Resolve browser polyfills from web_ui

Lib and plugins import Node.js modules such as events and buffer, which
the build swaps for browser packages. Vite resolves an aliased import
from the importing package, and pnpm only lets a package see its own
dependencies, so the polyfills had to be dependencies of lib.

Resolve them from web_ui with a small resolver plugin instead, also
used by the dependency optimizer. Hosts no longer install the browser
packages, and plugins get the same polyfills webpack gave them.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/devs/plugin-migration-to-2.1.md

@@ -54,7 +54,6 @@ These are left as imports in the plugin bundle and resolved by the browser, ther
 Everything else is bundled into the plugin, including `@ant-design/icons`.
 Import `react-dom/client` and `react/jsx-runtime` by those names, other subpaths of the shared packages are bundled as a separate copy.
 
-Vite does not provide Node.js modules to plugin code.
-If your web code imports `events`, `path` or similar, add the browser package for it (`events`, `path-browserify`) to your dependencies.
+Imports of `assert`, `buffer`, `events`, `os`, `path`, `process`, `stream`, `util` and `zlib` resolve to the same browser packages as before, provided by `@clusterio/web_ui`.
 
 The `container` property of `WebPluginContext` is now the plugin's ES module namespace, `await container.get("./web")` returns the module instead of a factory function.