fix: use startsWith('Sales') for party labels in print templates

Templates hard-coded `doc.entryType === 'SalesInvoice'` to determine
party labels (Customer/Supplier, To/From) and the document heading
(Invoice/Bill). This caused SalesQuote, PurchaseOrder, and other
entry types to fall through to the wrong label.

- Business template: use `doc.entryLabel` for the heading instead of
  hard-coded 'Invoice'/'Bill', and `startsWith('Sales')` for the
  Customer/Supplier label
- Minimal template: use `startsWith('Sales')` for the To/From labels

Fixes frappe/books#1399

templates/Business.template.html

@@ -26,9 +26,7 @@
     <div class="mt-8 text-lg">
       <!-- Doc Details -->
       <section class="flex">
-        <h3 class="w-1/3 font-semibold">
-          {{ doc.entryType === 'SalesInvoice' ? 'Invoice' : 'Bill' }}
-        </h3>
+        <h3 class="w-1/3 font-semibold">{{ doc.entryLabel }}</h3>
         <div class="w-2/3 text-gray-800">
           <p class="font-semibold">{{ doc.name }}</p>
 
@@ -42,7 +40,7 @@
       <!-- Party Details -->
       <section class="mt-4 flex">
         <h3 class="w-1/3 font-semibold">
-          {{ doc.entryType === 'SalesInvoice' ? 'Customer' : 'Supplier' }}
+          {{ doc.entryType.startsWith('Sales') ? 'Customer' : 'Supplier' }}
         </h3>
 
         <div class="w-2/3 text-gray-800" v-if="doc.party">

templates/Minimal.template.html

@@ -35,7 +35,7 @@
     <!-- Party Details -->
     <section class="w-1/2">
       <h3 class="uppercase text-sm font-semibold tracking-widest text-gray-800">
-        {{ doc.entryType === 'SalesInvoice' ? 'To' : 'From' }}
+        {{ doc.entryType.startsWith('Sales') ? 'To' : 'From' }}
       </h3>
       <p class="mt-4 text-black leading-relaxed text-lg">{{ doc.party }}</p>
       <p
@@ -64,7 +64,7 @@
           ml-8
         "
       >
-        {{ doc.entryType === 'SalesInvoice' ? 'From' : 'To' }}
+        {{ doc.entryType.startsWith('Sales') ? 'From' : 'To' }}
       </h3>
       <p class="mt-4 ml-8 text-black leading-relaxed text-lg">
         {{ print.companyName }}