I have been made aware that rule 711.4a states that ingame all cards only have the characteristics of their front face, but that doesnt refer to deckbuilding.
For purposes of C.R. 712.4a and Zirda's companion ability, at the moment you determine whether a card meets the requirements of Zirda's companion ability, a card in your starting deck is in your library, and thus inside the game (C.R. 103.2, 103.2b-c, 400.11).
Thus, for example, neither Nissa nor Growing Rites of Itlimoc has any activated abilities for this purpose since neither card is on the battlefield or the stack and neither card's front face has any activated abilities, so neither card can be included in your deck if you want to reveal Zirda as "your companion".
To be clear, a card with a basic land type "has an activated ability" for the purposes of Zirda's companion ability, even if the only activated abilities it has are those it inherently has for having a basic land type (C.R. 305.6, 602.1).
EDIT (Apr. 17): Edited to conform to rule update with Ikoria: Lair of Behemoths.
EDIT (Aug. 17, 2021): Edited generally, including for correctness and to conform with rule updates in the meantime.
EDIT (Oct. 3, 2021): Correctness edit.
EDIT (Oct. 18, 2021): Edited.
I don't believe that this has been directly clarified yet, but there are parralels that can be drawn with other things, mainly in commander which has built-in deckbuilding rules based on the characteristics of the cards (I know you're asking about commander, but this will be relevant for other formats as well). For example, you can't play Westvale Abbey as your commander, because its front face is not a creature. By that logic, no, Nissa or Growing Rites won't count.
Westvale Abbey's color identity is black, so its back face is not ignored for that, so it could lead you to believe that companions will follow the same logic, but looking at the color identity rules shows us that color identity is a very specific exception:
903.4c. The back face of a double-faced card (see rule 711) is included when determining a card's color identity. This is an exception to rule 711.4a.
It even specifies that it is an exception to rule 711.4a that you mentionned. So unless another specific exception is included in the rules, it is the logic of 711.4a that will apply, even if it doesn't seem to be about deckbuilding.
711.4a. While a double-faced card is outside the game, in a zone other than the battlefield, or on the battlefield with its front face up, it has only the characteristics of its front face.
I would argue that "outside the game" emcompasses deckbuilding rules, but adding a clarification about this in the rules might be a good thing to suggest to Rules Manager Eli Shiffrin, I don't know.
I'm a former judge (lapsed), who keeps up to date on rules and policy. Keep in mind that judges' answers aren't necessarily more valid than those of people who aren't judges; what matters is we can quote the rules to back up our answers. When in doubt, ask for such quotes.
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I have been made aware that rule 711.4a states that ingame all cards only have the characteristics of their front face, but that doesnt refer to deckbuilding.
For purposes of C.R. 712.4a and Zirda's companion ability, at the moment you determine whether a card meets the requirements of Zirda's companion ability, a card in your starting deck is in your library, and thus inside the game (C.R. 103.2, 103.2b-c, 400.11).
Thus, for example, neither Nissa nor Growing Rites of Itlimoc has any activated abilities for this purpose since neither card is on the battlefield or the stack and neither card's front face has any activated abilities, so neither card can be included in your deck if you want to reveal Zirda as "your companion".
To be clear, a card with a basic land type "has an activated ability" for the purposes of Zirda's companion ability, even if the only activated abilities it has are those it inherently has for having a basic land type (C.R. 305.6, 602.1).
EDIT (Apr. 17): Edited to conform to rule update with Ikoria: Lair of Behemoths.
EDIT (Aug. 17, 2021): Edited generally, including for correctness and to conform with rule updates in the meantime.
EDIT (Oct. 3, 2021): Correctness edit.
EDIT (Oct. 18, 2021): Edited.
Westvale Abbey's color identity is black, so its back face is not ignored for that, so it could lead you to believe that companions will follow the same logic, but looking at the color identity rules shows us that color identity is a very specific exception: It even specifies that it is an exception to rule 711.4a that you mentionned. So unless another specific exception is included in the rules, it is the logic of 711.4a that will apply, even if it doesn't seem to be about deckbuilding. I would argue that "outside the game" emcompasses deckbuilding rules, but adding a clarification about this in the rules might be a good thing to suggest to Rules Manager Eli Shiffrin, I don't know.