feat: move action icon into URL bar

[jceb]

Closes #10

I'm not sure about this change since a) Chrome doesn't support icons in the URL bar :-/ and b) Firefox doesn't seem to support the full color palette as one can see on the screenshots.

Firefox:

Chrome:

[simne7]

Hm 🤔

• we could adjust the color palette for FF. your screenshot shows at least some red and blue icons... but for a good UX at least some red, orange, green, and gray palette should be possible
• as Chrome does not support it at all: should we probably stay with what we have to keep a consistent UI across browsers? Helps us as devs (less code to maintain) and users using both browsers