fix(admin): restore webpack build on Shopware 6.6 - #480

1. Why is this change necessary?

Since 3.15.0, the webpack build of the FroshTools administration fails on Shopware 6.6 with 8 errors. Any build that compiles the plugin source is affected, for example shopware-cli project admin-watch or bin/watch-administration.sh. There are two causes.

• src/Resources/app/administration/package.json declares "type": "module". Webpack then treats every .js file as strict ESM and only accepts fully specified imports. fix: use fully specified imports in administration for strict ESM builds #471 fixed this for 3.14.1. Four imports added in Fix health indicator layout on Shopware 6.7.15 sidebar #465 and feat: add Apps section with shop reachability, store login and shop id reset #467 have no extension again ('../../acl/privileges' and '../override-if-exists'). The release zip is built with esbuild, which accepts these imports, so the error only appears in projects that build the plugin with webpack.
• Shopware's webpack config provides process as process/browser through ProvidePlugin and resolve.fallback. Webpack resolves that request from the importing file. debug and kleur come in through mermaid, and both sit in the plugin's own node_modules. No process package is installed there. kleur/index.mjs is strict ESM, so process/browser would fail even if process were installed.

Module not found: Error: Can't resolve '../../acl/privileges' in '.../component/frosh-tools-health-status'
Did you mean 'privileges.js'?
BREAKING CHANGE: The request '../../acl/privileges' failed to resolve only because it was resolved as fully specified

Module not found: Error: Can't resolve 'process/browser' in '.../administration/node_modules/kleur'

2. What does this change do, exactly?

• Adds .js to the relative imports in frosh-tools-health-status/index.js, frosh-tools-tab-apps/index.js, overrides/sw-admin-menu/index.js and overrides/sw-version/index.js.
• Adds src/Resources/app/administration/build/webpack.config.cjs. It aliases process/browser$ to the administration's own process/browser.js, resolved from the webpack working directory. An absolute path also satisfies fully specified ESM. The file uses .cjs because the package is "type": "module". Shopware's BundleConfigGenerator and shopware-cli both detect build/webpack.config.cjs. The Vite build on 6.7 ignores the file.

"type": "module" stays in place.

3. Describe each step to reproduce the issue or behaviour.

1. Set up a Shopware 6.6 project, which builds the administration with webpack, and install FroshTools 3.15.0.
2. Run shopware-cli project admin-watch. It installs the plugin's npm dependencies and compiles the plugin source.
3. Before: webpack stops with 8 errors. Four are "fully specified" import errors, two are process/browser errors, and two are the resulting Cannot read properties of undefined (reading 'module') errors.
4. After: webpack logs # Plugin "FroshTools": Extends the webpack config successfully and compiles without errors.

Shopware 6.7 builds the administration with Vite and is not affected.

4. Please link to the relevant issues (if any).

Follow-up to #471 (#468). The extensionless imports came back in #465 and #467.