Beautiful plant, but be very careful. It can be extremely difficult to remove from unwanted areas. A raised border planter won't necessarily be sufficient to contain spread--it can send rhizomes down and then laterally. (Picture down a raised planter and under a 3-4' concrete walkway.) If brave enough, I would put it in a solid bottomed planter with just drainage holes below, on top of solid concrete. And then be very careful with the pruning pieces. Definitely do not reuse the soil. I love the look of the plant, but don't dare introduce it into my CA garden.

Yup, agreed on the ID. You could probably take cuttings a few nodes long & pot them back into mother plant's pot, to make it look even more full & lush.

Yes: it's a Helianthus. There are several dwarf/bushy hybrid cultivars that are mostly grown as annuals (although I believe they can overwinter in zones 9 and above), and this looks pretty similar to the 'Suncredible' series that are pretty popular in garden centers thesse days: https://www.lsuagcenter.com/articles/page1623084762361

I've heard Alkanet mentioned in a British gardening group, but I doubt most Americans have heard that name. It sounds very similar to Comphrey. It has agressive rhyzomes and it's an excrllent addition to compost. I searched to see what chemical caused skin irritation, rashes and blisters and it has no toxic chemicals it's the hairs themselves that cause blisters. Maybe Alkanet had convergant evolution with tarrantulas that use their hairs as a defense Lol. What exactly do Comphrey and Alkanet posess that makes them so beneficial for compost?