SunbeamError enum with typed variants (Kube, Config, Network, Secrets,
Build, Identity, ExternalTool, Io, Json, Yaml, Other) each mapping to
a process exit code. ResultExt trait replaces anyhow's .context().
main.rs initializes tracing-subscriber with RUST_LOG env filter and
routes all errors to exit codes via SunbeamError::exit_code().
Removes anyhow dependency.
