I'm not familiar with CA code, but typically apartments and condos, any sort of a building that has a "common" water supply, does need a shutoff per unit or per fixture so that work can be done in a specific unit without having to shut down the water supply to the entire building.

We normally handle that by using shower valves with built in "stops".

Stops are small valves on the hot and cold supply sides of a shower valve. You need to work on the valve, you rotate the stops. Then the valve can be serviced.

Not sure if that'll fulfill your code requirement, or if you need a no kidding valve for the shower branch lines. You can ask your AHJ for clarification.

Before you proceed ensure you have interpreted the code correctly by confirming it's intent with the building department. Here a "main" shut off must be installed where the main supply line enters the unit, in some cases 1 each for hot and cold. If you are doing the replumb from scratch an independent shot off for each fixture would be a smart move regardless of code. I would run the supply lines for the tub, shower from below the bathroom sink where I can easily isolate the tub, shower. No need for a panel in that case.