I saw some of these in a street garden today, and fell in love with them.
The leaf is heart shaped like a violet and the little flowers are held
upright several inches above the foliage, and are the clearest most glorious
blue!

I want to add some to my garden. But I have some questions:

I know they multiply rapidly, but are they invasive?

How cold hardy are they?

Will they tolerate poor drainage (I have clay)

How long do the flowers last?

Does the foliage die back or last the season?

TIA.