AB#32538: Prevent creation of multiple Sites with Same Number

[aurelio-aot]

Addresses a PROD issue where a supplier could end up with multiple Site rows sharing the same Number.
Three fixes applied:

• UpsertSupplierHandler: Deduplicate incoming SiteEtos by SupplierSiteCode before the upsert loop — prevents duplicates when CAS returns duplicate site codes in a single event payload.
• SiteAppService.InsertAsync: Check for an existing site with the same SupplierId + Number before inserting. If found, update it instead — makes the method idempotent and guards against concurrent upsert calls.
• SupplierInfo.js: Disable the "Refresh Site List" button while the AJAX request is in flight and re-enable it on completion — prevents multiple concurrent refresh requests from being fired by rapid clicks.

[github-actions]

🧪 Unit Test Results (Parallel Execution)

📊 Summary

Result	Count
✅ Passed	575
❌ Failed	0
⚠️ Skipped	0

📄 HTML Reports

• Merged Tests (HTML): Included in artifacts
  Generated automatically by CI.

[github-actions]

🧪 Unit Test Results (Parallel Execution)

📊 Summary

Result	Count
✅ Passed	575
❌ Failed	0
⚠️ Skipped	0

📄 HTML Reports

• Merged Tests (HTML): Included in artifacts
  Generated automatically by CI.