How do I create "beveled" T-intersection traces in Eagle CAD?
Right below the "Route" tool is a "Wire" tool, which you are probably familiar with from the schematic editor.

You can use this to create arbitrary traces, such as short 45° segments to create a bevel:



You might have to change the grid pitch or hold Alt to start the wire at an appropriate location near the intersection. Make sure the wire bend style allows the angle or curve you want.

With just two wire segments you can create a simple 45° beveled "T" intersection like this: