Add typed JSON output to theme pull

[gonzaloriestra]

WHY are these changes introduced?

Related to https://github.com/shop/issues-develop/issues/23693

theme pull downloads files but does not expose a typed, discoverable JSON result for automation.

WHAT is this pull request doing?

Add --json with the local download path, remote theme metadata, and preview/editor links. Execution returns typed data; a presenter retains the existing success banner. The exported pull() adapter keeps its text behavior. Download progress uses typed side events in JSON mode.

Normal output:

The theme 'MyTheme' (#1) has been pulled.

Matching JSON:

{
  "path": "/path/to/theme",
  "theme": {
    "id": 1,
    "name": "MyTheme",
    "role": "unpublished",
    "processing": false,
    "shop": "example.myshopify.com",
    "editor_url": "https://example.myshopify.com/admin/themes/1/editor",
    "preview_url": "https://example.myshopify.com?preview_theme_id=1"
  }
}

Optional src metadata is included when available. The internal createdAtRuntime flag is not part of the public result.

Uses the draft multi-environment contract from the preceding PR: one array in requested order, environment names on successful results, failures on stderr, [] when none succeed, and unchanged exit behavior. Tests use real temporary files for downloads, deletion, and --nodelete.

How to manually test your changes?

pnpm shopify theme pull --help
pnpm shopify theme pull --json-schema
pnpm shopify theme pull --store example.myshopify.com --theme 1 --path ./theme --json
pnpm shopify theme pull --store example.myshopify.com --theme 1 --path ./theme --nodelete --json
pnpm shopify theme pull --environment staging --environment production --force --json

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, #8643.