feat: Add intelligent "Meaning" tool with dictionary/translation auto-detection

[nov3o]

Summary

• Replace separate Dictionary/Translate tools with unified "Meaning" tool
• Auto-detect: single words → Dictionary, phrases → Translation
• Fallback: Dictionary lookup fails → Translation mode available with language selection
• Manual switching with Dictionary/Translate tabs

[johnfactotum]

It's not clear to me what use case this would be advantageous for. Perhaps if you need to switch back and forth between different tools. It used to have a "tabbed" design like this, together with the Wikipedia tool, which is similar to the design used by Kindle. But I think the current design does have some advantage in its simplicity.

As for the implementation, for a design like this one it would probably be better to use the new AdwToggleGroup widget. Also for detecting multiple words one should probably use Intl.Segmenter or something like that. There are other problems as well, such as some labels seemingly not being translatable, and the HTML page is not added to the GResource list.