Add typed JSON output to theme init

[gonzaloriestra]

WHY are these changes introduced?

theme init clones a theme and optionally creates AI instructions without returning a typed result for scripts.

Part of shop/issues-develop#23694.

WHAT is this pull request doing?

Expose the destination, repository, latest-release option, selected AI instructions, and instruction file paths as JSON. Keep the existing prompts and cleanup behavior, report task progress and copy-fallback warnings on stderr, and emit the result only after setup completes.

Fix the existing --latest clone failure by disabling shallow cloning when fetching release tags.

Normal output:

Cloning https://github.com/Shopify/skeleton-theme.git into /themes/example

Matching JSON example when AI setup is skipped:

{
  "path": "/themes/example",
  "repoUrl": "https://github.com/Shopify/skeleton-theme.git",
  "latest": false,
  "aiInstructions": null,
  "instructionFiles": []
}

How to manually test your changes?

pnpm shopify theme init example
pnpm shopify theme init example --json
pnpm shopify theme init example --clone-url https://github.com/Shopify/dawn.git --latest --json
pnpm 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
• A single changeset for all theme migrations is added in the last PR, #8682.

[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

@@ -35,6 +35,7 @@ declare abstract class BaseCommand extends Command {
         argv: string[];
     }>;
     protected environmentsFilename(): string | undefined;
+    protected validateNonTTYFlags(flags: FlagOutput): void;
     protected failMissingNonTTYFlags(flags: FlagOutput, requiredFlags: string[]): void;
     private failMissingNonTTYFlagRequirements;
     private applicableNonTTYFlagRequirements;