Electronic – What cause a PCB track to break

The easy way:

Keep your design as-is.

The wavelength at 1800 MHz is 167 mm. Your track length is 10 mm. This is less than 1/10 wavelength so you can probably get away with not worrying too much about controlled impedance on this line. Certainly the few mm of necked-down trace at the pad end of your track are not going to be a big problem.

The hard way:

If you use a thinner dielectric, the required trace width will get narrower (certainly for microstrip geometry, probably also for CPW but I haven't double-checked this). You could either switch to something like a 1 mm dielectric thickness to get a slightly narrower trace width, or make a 4-layer board to get full freedom to choose your dielectric thickness. If you go with a 4-layer board, choose the dielectric thickness (of the microstrip/CPW structure) to give you a trace width that matches the pad width.

Bare hands should be sufficient. Grab the boards solidly and bend. Do so in a consistent fluid motion, and hold them such that the boards themselves won't bend much. You might have to work the seam in the opposite direction a few times to make them separate.

There are depanelling tools for these sorts of things, in the form of vertical wedge presses, or wheels similar to pizza cutters, but you only really need those for situations where you can't bend without damaging the boards, or when dealing with large quantities.

Doing it by hand is fine.