Surface Merchant Center setup for service-based merchants who add physical products

[jimjasson]

Changes proposed in this Pull Request:

This PR provides a path for service-based merchants to connect their Merchant Center account after they have set up at least 1 physical product.

Closes GOOWOO-516: Surface MC setup for transitioned service-based merchants

Specifically, a new ServiceBasedMerchantHooks class listens for product lifecycle events and resets the cached IS_SERVICE_BASED_MERCHANT option so it is recalculated on the next admin page load:

• Product created/updated/untrashed — if the product requires shipping and the store is currently flagged as service-based, the flag is reset.
• Product trashed/deleted — if the store is currently flagged as product-based, the flag is reset so it can be recalculated in case all physical products have been removed.

Moreover, a new ConnectMerchantCenterCard component was added in the Linked Accounts section of the Settings page.

It renders when:

• serviceBasedMerchant is false (merchant now has physical products), and
• MC is not yet connected

The card uses the existing MC account card appearance and links to the /google/setup-mc onboarding wizard, which will show the full MC + Ads stepper since the merchant is no longer service-based.

Once serviceBasedMerchant flips back to true (all physical products removed) or MC is connected, the card hides automatically.

Screenshots:

Detailed test instructions:

1. Start on a new site with 0 products.
2. Complete the Ads-only onboarding.
3. Create a physical product (non-virtual, requires shipping).
4. Navigate to Marketing -> Google for WooCommerce -> Settings.
5. Verify the MC setup card appears in the Linked Accounts section
6. Click "Set up Merchant Center" -> verify it navigates to the MC setup wizard.
7. Complete setup.

Changelog entry

Add - Added an option to connect a Merchant Center account when a service-based user adds physical products.

[codecov]

Codecov Report

❌ Patch coverage is 96.15385% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 66.6%. Comparing base (3cdbfb7) to head (f878c2a).

Files with missing lines	Patch %	Lines
...ernal/DependencyManagement/CoreServiceProvider.php	0.0%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             develop   #3298      +/-   ##
============================================
+ Coverage       66.1%   66.6%    +0.4%     
- Complexity         0    5247    +5247     
============================================
  Files            374     890     +516     
  Lines           6115   26923   +20808     
  Branches        1551    1551              
============================================
+ Hits            4045   17922   +13877     
- Misses          1870    8801    +6931     
  Partials         200     200              

Flag	Coverage Δ
js-unit-tests	66.1% <ø> (ø)
php-unit-tests	66.7% <96.2%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/Options/ServiceBasedMerchantHooks.php	100.0% <100.0%> (ø)
...ernal/DependencyManagement/CoreServiceProvider.php	0.0% <0.0%> (ø)

... and 514 files with indirect coverage changes

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