fix(vendor): show company values in business details placeholders

Added company_business_address and company_tax_number to:
- VendorDetailResponse schema
- API response builder

Template now shows actual company values as placeholders instead of
generic "Using company address/tax number" text.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/templates/admin/vendor-edit.html

@@ -323,7 +323,7 @@
                         x-model="formData.business_address"
                         rows="3"
                         :disabled="saving"
-                        :placeholder="!formData.business_address ? 'Using company address' : 'Enter business address'"
+                        :placeholder="vendor?.company_business_address || 'No company address'"
                         class="block w-full mt-1 text-sm dark:text-gray-300 dark:border-gray-600 dark:bg-gray-700 focus:border-purple-400 focus:outline-none focus:shadow-outline-purple dark:focus:shadow-outline-gray form-textarea"
                         :class="{ 'border-purple-300 dark:border-purple-600': !formData.business_address }"
                     ></textarea>
@@ -352,7 +352,7 @@
                         type="text"
                         x-model="formData.tax_number"
                         :disabled="saving"
-                        :placeholder="!formData.tax_number ? 'Using company tax number' : 'Enter tax number'"
+                        :placeholder="vendor?.company_tax_number || 'No company tax number'"
                         class="block w-full mt-1 text-sm dark:text-gray-300 dark:border-gray-600 dark:bg-gray-700 focus:border-purple-400 focus:outline-none focus:shadow-outline-purple dark:focus:shadow-outline-gray form-input"
                         :class="{ 'border-purple-300 dark:border-purple-600': !formData.tax_number }"
                     >