Handle a conflict between a generated file and a hand edit

Problem/Motivation

Refusing to write is only half an answer: the person now has a file the generator will not update and no path forward. Three ways out have to exist, and without them "the generator stopped touching my file" becomes a frozen endpoint nobody remembers freezing.

Proposed resolution

• A conflict entry in the queue with the diff between what is on disk and what would be written.
• Take generated — shows the diff, overwrites on confirmation, and says on the button that the edit will be lost.
• Keep mine — marks the file frozen, never touched again, with a standing warning that the endpoint is behind the model.
• Move to a subclass — shows which class to create and what to put in it, then returns the file to the generator.
• Frozen files listed on the status page, because the cost of freezing is invisible six months later.

Remaining tasks

Everything.