feat(cli): exec and logs pick a lease when you do not name one

[jleni]

Finishes what #387 started for vnc. kobe exec and kobe logs take
[LEASE]: with one lease that can serve the verb it is used, with several you
pick from a list, with none you are told so. Only leases advertising the verb
are offered.

$ kobe exec -- uname -a          # one exec-capable lease: used
$ kobe logs                      # several: picker
$ kobe exec -- uname -a          # none: "No active lease supports `exec`"

Non-interactive callers are unaffected — #387 put the terminal check inside
run_picker, so a script or an agent gets the candidates and how to name one
rather than a hang.

port-forward cannot join them

Not a decision — clap rejects it:

Found non-required positional argument with a lower index than a required
positional argument: "lease" index Some(1)

spec is a positional that follows the lease. Making the lease optional needs
spec to become a flag or the two to swap places, and both break a command
line people already use. Recorded on the field so the next person does not
rediscover it by hitting the assert at runtime.

exec works because -- already separates its trailing command:
kobe exec [OPTIONS] [LEASE] -- <COMMAND>....

Left out deliberately

cancel still requires its lease. A picker there means one mis-aimed keypress
cancels a lease, so it wants a decision on confirmation first.

Verification

213 unit + 48 integration tests, clippy -p kobectl --all-targets --all-features -D warnings clean. --help checked for all three:

kobe exec [OPTIONS] [LEASE] -- <COMMAND>...
kobe logs [OPTIONS] [LEASE]
kobe port-forward [OPTIONS] <LEASE> <SPEC>