Fix Company Settings save, invoice PAID stamp, and purge script

- Company Settings: switch save button from type=submit to type=button
  to bypass HTML5 form validation blocking the submit event; replace
  AutoMapper Map() with explicit property assignment so EF change
  tracking reliably detects mutations; fix showButtonSuccess() never
  re-enabling the button after a successful save
- Invoice PDF: move PAID stamp into the header row as a centered middle
  column so it sits between the company and invoice blocks without
  adding height to the document
- Purge script: use business-date fields instead of CreatedAt so
  imported records (which all share today's CreatedAt) are correctly
  filtered by actual transaction dates

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Web/Views/CompanySettings/Index.cshtml

@@ -312,7 +312,7 @@
                         </div>
 
                         <div class="d-flex justify-content-end">
-                            <button type="submit" class="btn btn-primary" id="btnSaveCompanyInfo">
+                            <button type="button" class="btn btn-primary" id="btnSaveCompanyInfo">
                                 <i class="bi bi-save"></i> Save Changes
                             </button>
                         </div>
@@ -2749,10 +2749,8 @@
                 }
             });
 
-            // Company Info Form Submit
-            $('#companyInfoForm').on('submit', function (e) {
-                e.preventDefault();
-
+            // Company Info Save
+            $('#btnSaveCompanyInfo').on('click', function () {
                 const formData = {
                     CompanyName: $('#companyName').val(),
                     CompanyCode: $('#companyCode').val(),
@@ -3192,7 +3190,7 @@
 
             // Button success animation helper
             function showButtonSuccess(btn, originalHtml, duration = 2000) {
-                btn.removeClass('btn-primary').addClass('btn-success');
+                btn.prop('disabled', false).removeClass('btn-primary').addClass('btn-success');
                 btn.html('<i class="bi bi-check-circle-fill"></i> Saved!');
                 setTimeout(function() {
                     btn.removeClass('btn-success').addClass('btn-primary');