Replaces the breadbar-only hardcoded view list with a registry keyed by
app name (--app-name, defaulting to --app-path's file stem) so wiring up
each new app just means adding one entry, not touching the CLI shape.
Also fixes a real leak found while testing breadbox against this:
std::process::exit() on the failure path skipped every destructor,
including Isolation's Drop — so a failed capture run (or, more subtly,
*any* run against an app whose view list didn't match yet, which is
exactly what happened testing this) permanently orphaned the headless
Sway process and its wayland-N/.lock socket pair. main() now returns
ExitCode instead of calling process::exit directly, so Drop always runs.
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