CC-40102 Merchant profile Backend API

[demkos]

PR Description

Documents the merchant profile Backend API shipped with spryker/suite#1142:

• Backend API: Retrieve merchant profiles — GET /merchant-profile (merchant user, merchant resolved from the token) and GET /merchant-profiles/{merchantReference} (Back Office user), with a shared response-attributes include.
• Backend API: Update merchant profiles — PATCH on both routes; partial-update rules for localizedAttributes (per-locale replace) and addresses (upsert by uuid, no delete); the 1301–1305 error codes.
• Install the Merchant Profile Backend API — module versions, the optional Uuid feature of MerchantProfile (isUuidEnabled() override, propel:install, uuid:generate backfill), resource generation and verification.
• Sidebar entries (Manage via Backend API, install guide) and links from the merchant Glue API landing page.

Stacked on #3899 (the pages link to the new merchant user authentication page); retarget to master after that PR merges. Ready for review once spryker/suite#1142 is merged; opened as a draft until then.

Scope note: everything documented here requires the API Platform integration of the Backend API; the legacy Glue infrastructure is not covered, and every page says so in an info block.

Tickets

CC-40102 — https://spryker.atlassian.net/browse/CC-40102 (code: spryker/suite#1142)

Checklist

• I agree with the Code Contribution License Agreement in CONTRIBUTING.md
• I validated and improved the content with Custom GPT
• I checked my pages at the deployment preview website.
• I invited a person to review and merge this PR.