refactor: modernize codebase, remove Angular and legacy dependencies

[robertodauria]

Summary

• Remove Angular 1.x, jQuery, Gulp, Bower, Skel framework
• Replace with vanilla JS (app.js, gauge.js, i18n.js)
• Add runtime i18n with ?lang= query param support
• Simplify CSS from ~4000 to ~900 lines
• Add simple Node.js build script (scripts/build.js)
• Convert .po translations to JSON format
• Update GitHub Actions workflows for new build
• Change Firebase public dir from app/ to dist/

Dependencies reduced from ~680 to 13 packages.

Closes #42, #40, #36, #111, #147, #152

[bassosimone]

I like the approach of picking the axe (cit.) and significantly simplifying, refactoring, and rationalizing the website. Thank you for doing this!

I do not think this branch is ready for merge. I have a bunch of questions and aspects that I find slightly troubling. I think we need to discuss and resolve those points before we move forward.

[bassosimone]

I am not so amused that the generation happens as a side effect of importing. Could you please make this module such that we import w/o side effects and then we explicitly trigger the generation?

[github-actions]

Visit the preview URL for this PR (updated for commit 08f6f5d):

https://mlab-sandbox--pr-83-nx1hjbn2.web.app

_{(expires Mon, 02 Mar 2026 00:34:45 GMT)}

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