POS UI Extensions: migrate shopify.extension.toml — add api_version and explicit targets

[mohab-sameh]

Config format updated; missing api_version/targets breaks builds. (Shopify)

Before (partial)

[[extensions]]
type = "ui_extension"
# no api_version / targets declared

After (partial)

api_version = "2025-04"

[[extensions]]
type = "ui_extension"
[[extensions.targeting]]
target = "pos.home.modal.render"

Detect:

• shopify.extension.toml with no api_version.
• Missing [[extensions.targeting]] (or old target syntax).

Edge cases:

• Multiple targets per extension—don’t overwrite existing ones; append.

Reference:

• POS UI Extensions “Configuration” section:

  https://shopify.dev/docs/api/pos-ui-extensions/latest/migrating#configuration (Shopify)