Add basic localization support using YAML files and language selector

[Cassutti]

This PR introduces a basic localization system to Onboarderr using external YAML files stored in a locales/ folder.

Key Features

• Language strings in onboarding.html are now loaded from a locales/{lang}.yaml file (currently only en.yaml included).
• A language selector () was added to the top-right corner of the onboarding page. Language loading logic added in app.py. How to add a new language Duplicate locales/en.yaml and rename it (e.g., locales/it.yaml). Translate only the values, keeping the keys unchanged. Add the new language option in the dropdown inside onboarding.html.

[secretlycarl]

thanks for this! will try to add it for v2, or include soon after v2.

[Cassutti]

Added it.yaml for Italian translation

[secretlycarl]

@Cassutti I haven't worked on this yet, but wanted to let you know v2 (style overhaul) is almost done.

#20

should be able to pull it on a new clone of the main branch like

git switch style-overhaul

pull that and you can test it out, the repo screenshots arent updated but setup is a lot easier now. re-read the new readme for new instructions

[Cassutti]

i'll give it a look