[M6] Design strongly typed SDK operation results

[GaTTGeng]

Summary

Design a strongly typed managed SDK surface so callers do not need to interpret CLI-shaped CommandResult output for most operations.

Scope

• Inventory IHelmClient operations and classify suitable result types.
• Define typed success models and a consistent error model.
• Represent warnings and diagnostics.
• Cover release, history, manifest, values, status, package, and repository results.
• Define a non-breaking 1.x compatibility strategy.
• Document a 2.0 migration path if breaking changes are required.

Acceptance Criteria

• The proposal covers success, warnings, cancellation, validation, and Kubernetes failures.
• Existing 1.x consumers have a migration path.
• New typed APIs do not require parsing StandardOutput.
• CLI-compatible and managed SDK methods have clear roles.
• Implementation can be split into focused follow-up issues.