feat: add read-only configuration commands

[JacobPEvans-personal]

Summary

• add config list and config get commands over Splunk search-head REST
• apply namespace resolution, path validation, pagination, and secret redaction
• register both reads in the shared CLI catalog
• document the new command surface

Validation

• pre-commit commit-stage and pre-push gates passed
• 1045 tests passed; 249 credential-gated tests skipped
• public ACS OpenAPI contract test passed
• nix flake check --no-build passed

Refs #7

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