Add typed JSON output to theme publish

[gonzaloriestra]

WHY are these changes introduced?

theme publish has no JSON result contract, so automation must parse terminal output.

Part of shop/issues-develop#23692.

WHAT is this pull request doing?

Return the published API theme as typed data and move final output into a presenter. Reuse the environment collector from the preceding PR, retaining prompts and the original terminal wording. Add --json, expose the domain-owned schema, and refresh the manifest, README, and generated docs.

Normal output includes:

The theme 'Original' (#1) is now live at https://example.myshopify.com.

Matching JSON:

{
  "theme": {
    "id": 1,
    "name": "Original",
    "role": "live",
    "processing": false,
    "createdAtRuntime": false,
    "shop": "example.myshopify.com"
  }
}

The optional src field is retained when present. Multiple environments return {"environments":[{"environment":"staging","result":...}]} in configured order. Failed or invalid environments are omitted and reported on stderr; total failure returns an empty array. Existing exit behavior and single-environment presentation are preserved.

How to manually test your changes?

pnpm shopify theme publish --help
pnpm shopify theme publish --json-schema
pnpm shopify theme publish --store "$STORE" --theme "$THEME_ID" --force
pnpm shopify theme publish --store "$STORE" --theme "$THEME_ID" --force --json
pnpm shopify theme publish --environment staging --environment production --theme "$THEME_ID" --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.