You will get multiple suggestions for this situation. I wish the question was asked
before materials were purchased but here goes my take:
We use DensArmor (not a error). Butt your joints
wherever they end up, no need to have them in a specific place. Now use Kerdi to just before where the tile will end as it should go a row or two outside of where the door will be. You have now waterproofed the entire INSIDE of the shower stall. Good to go. If the DensArmor/drywall joint is
outside of the tile, you just finish the seam as you would any drywall joint. If it's within the tiled area, the Kerdi will cover the joint and subsequent leftover drywall.
Alternatively, you could use CBU but now your seam
must be within the tiled area. Kerdi as above.
Unfortunately you chose Denshield. You could finish same as the CBU scenario but now you need a liquid waterproofer over the seams and screw holes. I'm personally not a fan of liquid waterproofing. You could still use Kerdi but that over the Denshield is a point of controversy.
Stay tuned for other ideas