Replace generateUnionEnums with unified enumStyle option

[Upgrade220]

Closes #1040

Problem

The library currently exposes generateUnionEnums as a boolean flag to switch enum output to union types. PR #1281 proposes adding a second boolean generateConstObjectEnums for as const object output. I think adding a second independent boolean is the wrong direction — two mutually exclusive flags that silently override each other is confusing API design, and it still leaves a gap: ContentType in the http-client is always emitted as a traditional enum regardless of what the user configures, making the output inconsistent.

Proposal

I propose replacing both flags with a single unified enumStyle option:

enumStyle?: "enum" | "union" | "const"
// default: "enum"

This makes the three output modes explicit and mutually exclusive by construction. generateUnionEnums is preserved as a deprecated alias — it still works and emits a runtime warning pointing users to the new option, so nothing breaks for existing consumers.

I also propose extending the "const" style to cover ContentType in the http-client templates. When enumStyle: "const" is set, ContentType is emitted as:

export const ContentType = {
  Json: "application/json",
  ...
} as const;
export type ContentType = (typeof ContentType)[keyof typeof ContentType];

This makes the entire generated output consistent — schema enums and internal http-client constants follow the same pattern.

Changes

• New enumStyle: "enum" | "union" | "const" config option and --enum-style CLI flag
• generateUnionEnums: true auto-promotes to enumStyle: "union" with a deprecation warning
• "const" style generates as const objects with a companion type alias for all schema enums
• "const" style also converts ContentType in both Axios and Fetch http-client templates
• enum-data-contract.ejs subtemplate updated to support all three styles
• Ts.Keyword.Const added for template authors who use codeGenConstructs
• Snapshot test added for enumStyle: "const"

---

Summary by cubic

Replaces generateUnionEnums with a unified enumStyle option ("enum" | "union" | "const") to control enum output, and applies the "const" style to ContentType in Axios and Fetch clients. Adds a CLI flag, deprecates the old option with a warning, keeps the default as "enum", and fixes an internal export leak for const enums.

• New Features

  • Added enumStyle ("enum" | "union" | "const") and --enum-style CLI flag; generateUnionEnums remains as a deprecated alias that auto-promotes to enumStyle: "union" with a warning.
  • "const" style emits as const objects with a companion type alias and updates ContentType in both clients; parsers/discriminator handling/templates updated; snapshot tests added.

• Bug Fixes

  • const handler now respects internal and does not export the type alias for internal contracts.

^{Written for commit cb32443. Summary will update on new commits. Review in cubic}

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🦋 Changeset detected

Latest commit: cb32443

The changes in this PR will be included in the next version bump.

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Name	Type
swagger-typescript-api	Minor

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[cubic-dev-ai]

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