Yes, a Magus can use Dimension Door as part of Spell Combat
A full-round action is one of several different actions, but none of them are specifically broken up into standard-move action pairs, so there is no reason why Dimension Door's action restriction should apply beginning in the middle of any full-round action.
As in your question the magus would be able to begin the full-round action, cast the spell, attack, then end the full-round action without taking any "other actions" after casting the spell.
That being said, I'll leave my original answer below, provided that the glue working on creatures is the only house rule your DM made. Ultimately, it will be his or her call, though.
No, you can't break the connection with any kind of teleportation, unless the description of this teleportation explicitly states so.
The description of Sovereign Glue (DMG, p. 200) explicitly states:
Once it has done so, the bond it creates can be broken only by the application of universal solvent or oil of etherealness, or with a wish spell.
Specific overrules general, so even if you had a means of teleportation that stated something like "breaks any attachments to objects or creatures too large to teleport along", you couldn't teleport away from the glue.
However, I don't know of any means of teleportation that has something even remotely similar to this in its description, so according to RAW, the answer is clearly a strict No.
So, what are your other choices?
- use one of the means that are described in the description
- cut off your hand, or flay your hand
- cut out part of the wall
- remain there forever and die.
Mind you - Sovereign Glue is a legendary item, so it should be accordingly powerful.
In fact, your DM might even rule that chopping off your hand or carving out a piece of the wall is impossible, since you are glued to the wall, and that bond cannot be broken by any means other than those explicitly mentioned in the description.
Best Answer
No, you don't have to step through a door (magical or otherwise) to teleport. Dimension Door only has a Verbal component, and its duration is Instantaneous. So you say some magical words, and you're instantly teleported. The description doesn't say anything about a door; it's only the title that contains the word "door".
As for why the spell is called Dimension Door, this particular spell goes all the way back to OD&D (I believe it's been in every D&D edition), so the name in 5e is simply a legacy of previous editions.