Add typed JSON output to theme init

[gonzaloriestra]

Original PR and review history: #8684.

WHY are these changes introduced?

Fixes https://github.com/shop/issues-develop/issues/23694

Theme initialization needs structured outcomes that retain completed setup.

WHAT is this pull request doing?

Return an absolute project directory, instruction file paths and explicit success/partial outcomes. Keep a successfully cloned project when later AI setup fails, exit nonzero for partial work, and reject missing noninteractive names.

The public output follows docs/cli/json-output.md; explicitly named environments use one {environments: [...]} object.

How to manually test your changes?

shopify theme init example-theme --json
shopify theme init --json-schema

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add

[karreiro]

Thank you, @gonzaloriestra!

[github-actions]

⚠️ Potential Breaking Changes Detected

This PR contains changes that may break the existing contract.

@shopify/dev_experience — this PR contains breaking changes that require coordination for the next major release.

📦 Major Version Changesets

The following changesets request a major version bump:

Changeset	Package
theme-check-json-contract.md	'@shopify/cli': major
theme-preview-json-contract.md	'@shopify/cli': major
theme-profile-environments.md	'@shopify/cli': major

[github-actions]

Differences in type declarations

We detected differences in the type declarations generated by Typescript for this branch compared to the baseline ('main' branch). Please, review them to ensure they are backward-compatible. Here are some important things to keep in mind:

• Some seemingly private modules might be re-exported through public modules.
• If the branch is behind main you might see odd diffs, rebase main into this branch.

New type declarations

We found no new type declarations in this PR

Existing type declarations

packages/cli-kit/dist/public/node/base-command.d.ts

@@ -21,6 +21,7 @@ declare abstract class BaseCommand extends Command {
     static descriptionWithoutMarkdown(): string | undefined;
     static analyticsNameOverride(): string | undefined;
     static analyticsStopCommand(): string | undefined;
+    private jsonOutputFromFlags;
     catch(error: Error & {
         skipOclifErrorHandling: boolean;
     }): Promise<void>;
@@ -36,6 +37,7 @@ declare abstract class BaseCommand extends Command {
     }, TGlobalFlags extends FlagOutput, TArgs extends ArgOutput>(options?: Input<TFlags, TGlobalFlags, TArgs>, argv?: string[]): Promise<ParserOutput<TFlags, TGlobalFlags, TArgs> & {
         argv: string[];
     }>;
+    protected runWithParsedOutput<T>(flags: FlagOutput, execute: () => T): T;
     protected environmentsFilename(): string | undefined;
     protected parseEnvironmentFlags<TFlags extends FlagOutput, TGlobalFlags extends FlagOutput, TArgs extends ArgOutput>(environment: JsonMap, options: Input<TFlags, TGlobalFlags, TArgs>, explicitFlags: FlagOutput): Promise<FlagOutput>;
     protected validateNonTTYFlags(flags: FlagOutput): void;