[Epic][TypeSpec Authoring][Versioning] azure-typespec-author skill versioning support enhancement

## Summary
Track versioning support enhancement work for the `azure-typespec-author` skill.

When the skill makes changes to a TypeSpec service spec, it should **by default add the appropriate API version decorators** (e.g. `@added`, `@removed`, `@renamedFrom`, `@madeOptional`, `@typeChangedFrom`) to reflect those changes against the existing API versions, so that the generated spec remains versioning-correct without manual intervention.

## Motivation
Today the skill can produce spec edits that omit version decorators, which leads to versioning inconsistencies and breaking-change issues that must be fixed manually. Making decorator annotation the default behavior keeps multi-version specs correct and reduces reviewer/author burden.

## Goals
- By default, detect spec changes that require versioning decorators and apply them automatically.
- Support the common versioning decorators for add / remove / rename / optionality / type-change scenarios.
- Respect the service's existing `@versioned` enum and target the correct version.
- Validate the result with TypeSpec compilation / linting.

## Related
- Refactoring epic: #15652