While it may be true that one hours is not a sensible connection with a wheelchair, all of the following are definitely true as well:

• AA's conditions of carriage do not give them the right to deny boarding if you arrive at the gate 17 minutes ahead of your scheduled flight time (the 30 minute suggestion quoted by JDiver above is helpful advice, but not a requirement in the contract)
• A four hour mechanical delay forcing another overnight stay is AA's fault
• A 90 minute delay caused by AA maintenance is their fault, but doesn't really matter since it didn't affect the connection in IAH
• A further delay caused by IT systems is BA's fault
• All of these circumstances together add up to a totally miserable passenger experience

I think AA owes OP reimbursement for the first night's hotel, and also ought to provide a reasonably huge amount of goodwill compensation for the overall delay and misery caused by their repeated failures to be able to operate a reliable airline. None of that is required by contract or by law, but it's really what should happen regardless of any lectures to the OP about the original connection.

Depending on when OP ended up arriving in Berlin, BA may also owe compensation under EC 261/2004, but only if the actual arrival was more than 3 hours late than the original January 8 LHR->TXL flight was scheduled to arrive.

As to whether the agent or the OP was at fault for the police being called, we obviously don't have enough information. I've seen plenty of people behaving badly at airlines, and also seen agents threaten to call the police on people who were just justifiably upset by their treatment. We certainly know there's been instances in which the police have been called on people doing nothing more controversial than sitting in seats that they had a boarding pass for, but I do agree it's unusual to see the police being called and it's possible OP did something to cause that. The fact that the police just talked to OP and went on their way does seem to indicate that the OP's behavior did not cross any legal lines, and I don't think it really forgives AA for anything else that happened in this tale. More to the point, if the original GA had just waited until T-15 to process standbys and close the door, there would have been no need for the police to arrive in the first place.