Consistent entry points and naming for Claude Agent

[bamurtaugh]

As we're also aiming to make the CLI session entry points consistent (#296381), I think doing the same for Claude Agent makes sense.

It looks like the command is Chat: New Claude:

Should it be Chat: New Claude Session or Chat: New Claude Agent Session?

[TylerLeonhardt]

Brigit Murtaugh (@bamurtaugh) this is probably a command contributed by core and is in the format:

Chat: New {0}

Where the placeholder is whatever the name of the session is. I like the idea of changing this to:

Chat: New {0} Session

I feel like we have the term Session used in a few places.