feat: Only partially functional preview removed, CSS and JS refactor

[fsbraun]

This PR fixes the issue #299 by removing the bundled JS files and simplifying the CSS build process

1. Webpack bundles are removed, and the little JS logic needed for the UI is now dependency-free, plain Javascript (no jQuery). No more npm-induced dependencies.
2. Bootstrap CSS dependency has been removed. The UI element styling - especially the tabs when editing a plugin - are now fully integrated in the /private/sass folder.
3. CSS has been updated for compatibility with the upcoming UI design

The link/button's preview has been removed, since it regularly shows misleading previews due to the different styling of django admin and the site itself.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.13%. Comparing base (554418c) to head (f1a5532).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #301      +/-   ##
==========================================
+ Coverage   89.01%   89.13%   +0.12%     
==========================================
  Files         124      124              
  Lines        3386     3387       +1     
  Branches      288      288              
==========================================
+ Hits         3014     3019       +5     
+ Misses        254      252       -2     
+ Partials      118      116       -2     

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[fsbraun]

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[Copilot]

Pull Request Overview

This PR removes the webpack-bundled JavaScript files and simplifies the build process by eliminating npm dependencies and switching to plain JavaScript. The main changes include:

• Removal of webpack bundles and transition to dependency-free plain JavaScript
• Bootstrap CSS dependency removal with custom UI styling now fully integrated in the /private/sass folder
• CSS updates for compatibility with upcoming UI design changes
• Removal of the preview functionality for links/buttons due to misleading previews

Reviewed Changes

Copilot reviewed 53 out of 58 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
tools/tasks/*.js	Removed webpack, svg, and lint gulp tasks
private/js/*.js	Removed webpack configuration and all component JS files
djangocms_frontend/static//js/bundle..js	Removed webpack-generated bundle files
djangocms_frontend/static/*/js/grid.js	New plain JavaScript implementation replacing webpack bundle
private/sass/components/*.scss	Updated SCSS with new variables, button styles, and removed preview styles
djangocms_frontend/templates//admin/.html	Updated script references from bundles to plain JS files
package.json	Significantly reduced dependencies, removing webpack and related packages

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[Copilot]

The commented out @include visually-hidden; line should either be removed if it's no longer needed or properly implemented if it serves a purpose. Commented code can lead to confusion about intended behavior.

Suggested change

// @include visually-hidden;