Add companion capabilities system

Verification

• I searched for similar feature request and found none was relevant.

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This would allow a companion app to broadcast its capabilities to the watch. Then, the watch can hide features unsupported by the companion.

Description

I think this could be implemented by using an enum to represent the capabilities, and exposing a characteristic where a companion can send a CBOR array containing the features they support. That data can then be used when determining whether to show certain items.

This is useful because not all companions are able to support all the features, and having the button for that feature visible but doing nothing causes confusion among users and causes users to file feature requests for things that cannot be supported.

For example, ITD cannot support muting on calls because ModemManager isn't responsible for the audio and there is no way to mute a call specifically. I would have to mute the entire system, which is not ideal and would be very unreliable in terms of turning off when the ringing is over.

I do not know how feasible this is on the watch side, it would probably be a lot of work, but I think it would be a very useful feature.

Start by tracing how the watch currently receives companion data and decides which features or buttons to show; the issue does not name specific files or tests. Define the capability enum and CBOR characteristic, connect the received capabilities to feature visibility, and verify that unsupported actions are no longer presented.