Reworks the salvaged command module into a CommandSource(SecretSource)
registered as the third bundled source, composing with Bitwarden and
1Password through the apply_all() orchestrator — enable any combination
simultaneously. The original PR's secrets.provider single-selector is
deliberately dropped: multi-source is first-class and a mutually
exclusive provider switch would regress that.
- fetch() only fetches; precedence/override/conflicts/environ writes stay
in the orchestrator. ErrorKind classification + remediation hints.
- apply_command_secrets() kept as a legacy shim (parser/security helpers
unchanged: HERMES_SECRET_KEY data-only key passing, cross-key misroute
guard, base64-padding disambiguation, timeout + output cap, structured-
fields-only failure logging, stderr discarded).
- Dispatch tests rewritten for the registry path incl. an explicit
two-sources-compose test; selector tests removed with the selector.
- cli-config.yaml.example + docs page (command.md), secrets index entry.
- contributors mapping for mvalentin@valensys.net -> 0xr00tf3rr3t.
