Add Epson TM-T20II receipt printing (title/body/QR, no ESC/POS knowledge needed)

Custom ReceiptBuilder instead of the escpos gem -- its diacritics handling
needed the same manual UTF-8->CP852 encode call anyway, based on earlier
experiments in ~/test/epson/.

views/_navbar.erb

@@ -12,6 +12,9 @@
         <li class="nav-item">
           <a class="nav-link" href="/upload">Shipping labels</a>
         </li>
+        <li class="nav-item">
+          <a class="nav-link" href="/epson">Receipts</a>
+        </li>
       </ul>
       <span class="navbar-text me-2">Brother:</span>
       <div class="d-flex gap-1">

views/epson.erb

@@ -0,0 +1,15 @@
+        <form action="/epson/print" method="POST">
+          <div class="mb-3">
+            <label for="title" class="form-label">Title (bold, centered)</label>
+            <input name="title" class="form-control" type="text" id="title" />
+          </div>
+          <div class="mb-3">
+            <label for="body" class="form-label">Body text</label>
+            <textarea name="body" class="form-control" id="body" rows="8"></textarea>
+          </div>
+          <div class="mb-3">
+            <label for="qr" class="form-label">QR code content (optional)</label>
+            <input name="qr" class="form-control" type="text" id="qr" />
+          </div>
+          <button class="btn btn-secondary" type="submit">Print</button>
+        </form>