[Feature Request] Persist tool color individually at tool level

Feature Description

Right now, Flameshot has one global color setting that applies to every tool. If I pick red for the arrow tool, and then switch to the text tool and pick blue, the arrow tool now also uses blue.

I'd like each tool to remember its own color, independently of the others. For example:

• Set the arrow tool to red;
• Switch to the text tool and set it to blue;
• Switch back to the arrow tool → it should still be red, not blue.

This mirrors how tool size is already handled after #782.

Note: There was an earlier request for this, issue #356, which asked for both size and color to be persisted individually per tool. That issue was closed as a duplicate of issue #782 but the color part was never actually implemented.