New `crates/maestro/` umbrella binary hosts the CLI, daemon, and registry
behind Cargo features `cli`, `daemon`, `registry` (default = all three).
Library crates keep their structure; per-binary `main.rs` files are removed
and their dispatch logic is exposed as public functions:
- `maestro_cli::dispatch(command, config, registry_url)`
- `maestro_daemon::cli::dispatch(config, cmd)` (with public `DaemonCmd`/`ConfigureArgs`)
- `maestro_registry::run()`
Subcommand surface:
- `maestro list / spawn / attach / kill / set-registry / policy` (unchanged)
- `maestro daemon [run|configure]` (was `maestrod`)
- `maestro registry` (was `maestro-registry`)
Hard cutover — old binary names are not preserved.
Verified: default-feature build, plus `--no-default-features --features {cli|daemon|registry}`
each build clean with `-D warnings`.