With the exclamation mark and with the -e- ending on the word "konsentite," I grasped the adverbial nature of the word as being like, "We are in agreement!" (The adverbial phrase "in agreement" adverbially modifies the general verb "are" and gives the verb a more precise meaning.) However, I translated it as "Agree!," and thus I didn't figure out how the '-ite-' ending gave it a past tense flavor of "Agreed!" I suppose that "Agree!" would be "konsentu!" But, I cannot say that "konsentate!" is not also possible in some word order (I don't know for sure).
Yes, and also, when separated from a noun (in certain ways/contexts), would-be adjectives instead become adverbs in Esperanto. So when you find something beautiful, you might say Tio estas bela, or instead, you might say Bele or Estas bele, but in principle you would/should not say Bela or Estas bela by itself.
(This is one of the things I never liked much about Esperanto, in truth, and it does not make a lot of sense to me, but that's how it goes.)