Unified /labels page (badges, edit, preview), mnemonic ESC/POS parser for the raw receipt field

- Saved labels/receipts now show on one page instead of split across
  Shipping labels and Receipts, each with a badge for its type/printer,
  Edit (name+content, in place), Print, and Delete.
- ZPL labels get a real visual preview via Labelary's public render API;
  ESC/POS ones show their raw content (no good general preview for that).
- The Receipts free-text field only ever encoded whatever was typed as
  literal printable characters -- pasting mnemonic ESC/POS notation
  (ESC/GS/LF as command names, 0xNN as raw bytes) just printed as text
  instead of being interpreted. Added a small line-based parser for that
  notation (ReceiptBuilder#raw appends already-resolved bytes verbatim),
  verified byte-for-byte against an example with align/bold/barcode/cut.

views/_navbar.erb

@@ -18,6 +18,9 @@
         <li class="nav-item">
           <a class="nav-link <%= 'active' if request.path == '/epson' %>" href="/epson">Receipts</a>
         </li>
+        <li class="nav-item">
+          <a class="nav-link <%= 'active' if request.path.start_with?('/labels') %>" href="/labels">Labels</a>
+        </li>
       </ul>
       <% if request.path.start_with?('/brother') %>
         <span class="navbar-text me-2">Printer:</span>

views/epson.erb

@@ -17,8 +17,20 @@
 
         <hr class="mt-4">
 
-        <h5>Free text (already-formatted ESC/POS)</h5>
-        <p>Sent as-is (just reset + code page prefix and a trailing cut), no title/body template applied.</p>
+        <h5>Free text (ESC/POS mnemonic notation)</h5>
+        <p>
+          One instruction per line: <code>ESC</code>/<code>GS</code>/<code>FS</code>/<code>LF</code>/<code>CR</code>/<code>HT</code>/<code>NUL</code> as
+          command names, <code>0xNN</code> as a raw byte, anything else as literal text. Trailing <code># comment</code> is ignored. Example:
+        </p>
+        <pre class="bg-light p-2"><code>ESC a 0x01   # Align: Center
+Hello        # literal text
+LF
+ESC E 0x01   # Bold on
+World
+LF
+ESC E 0x00   # Bold off
+GS k 0x03 12345678 0x00   # EAN8 barcode
+GS V 0x00    # Full cut</code></pre>
         <form action="/epson/raw" method="POST">
           <div class="mb-3">
             <textarea name="content" class="form-control" rows="8" style="font-family: monospace;"></textarea>
@@ -34,22 +46,4 @@
           </div>
         </form>
 
-        <% if @labels && !@labels.empty? %>
-          <hr class="mt-4">
-          <h5>Saved receipts</h5>
-          <div class="list-group">
-            <% @labels.each do |label| %>
-              <div class="list-group-item d-flex justify-content-between align-items-center">
-                <%= label['name'] %>
-                <div class="d-flex gap-2">
-                  <form action="/labels/<%= label['id'] %>/print" method="POST">
-                    <button class="btn btn-sm btn-secondary" type="submit">Print</button>
-                  </form>
-                  <form action="/labels/<%= label['id'] %>/delete" method="POST">
-                    <button class="btn btn-sm btn-outline-danger" type="submit">Delete</button>
-                  </form>
-                </div>
-              </div>
-            <% end %>
-          </div>
-        <% end %>
+        <p class="mt-4"><a href="/labels">See saved receipts &rarr;</a></p>

views/label_edit.erb

@@ -0,0 +1,20 @@
+<h4>Edit label</h4>
+
+<% if @label['type'] == 'zpl' %>
+  <span class="badge bg-primary">ZPL &middot; Datamax</span>
+<% else %>
+  <span class="badge bg-info text-dark">ESC/POS &middot; Epson</span>
+<% end %>
+
+<form action="/labels/<%= @label['id'] %>" method="POST" class="mt-3">
+  <div class="mb-3">
+    <label for="name" class="form-label">Name</label>
+    <input name="name" class="form-control" type="text" id="name" value="<%= @label['name'] %>" />
+  </div>
+  <div class="mb-3">
+    <label for="content" class="form-label">Content</label>
+    <textarea name="content" class="form-control" id="content" rows="12" style="font-family: monospace;"><%= @label['content'] %></textarea>
+  </div>
+  <button class="btn btn-secondary" type="submit">Save</button>
+  <a href="/labels" class="btn btn-outline-secondary">Cancel</a>
+</form>

views/labels.erb

@@ -0,0 +1,39 @@
+<h4>Saved labels &amp; receipts</h4>
+
+<% if @labels.empty? %>
+  <p>Nothing saved yet -- use "Save as" on <a href="/upload">Shipping labels</a> or <a href="/epson">Receipts</a>.</p>
+<% else %>
+  <div class="list-group">
+    <% @labels.each do |label| %>
+      <div class="list-group-item">
+        <div class="d-flex justify-content-between align-items-start">
+          <div>
+            <% if label['type'] == 'zpl' %>
+              <span class="badge bg-primary">ZPL &middot; Datamax</span>
+            <% else %>
+              <span class="badge bg-info text-dark">ESC/POS &middot; Epson</span>
+            <% end %>
+            <strong class="ms-2"><%= label['name'] %></strong>
+          </div>
+          <div class="d-flex gap-2">
+            <form action="/labels/<%= label['id'] %>/print" method="POST">
+              <button class="btn btn-sm btn-secondary" type="submit">Print</button>
+            </form>
+            <a href="/labels/<%= label['id'] %>/edit" class="btn btn-sm btn-outline-secondary">Edit</a>
+            <form action="/labels/<%= label['id'] %>/delete" method="POST">
+              <button class="btn btn-sm btn-outline-danger" type="submit">Delete</button>
+            </form>
+          </div>
+        </div>
+
+        <div class="mt-2">
+          <% if label['type'] == 'zpl' %>
+            <img src="/labels/<%= label['id'] %>/preview.png" alt="preview" style="max-height: 150px;" onerror="this.remove()" />
+          <% else %>
+            <pre class="bg-light p-2 mb-0" style="max-height: 150px; overflow: auto;"><%= label['content'] %></pre>
+          <% end %>
+        </div>
+      </div>
+    <% end %>
+  </div>
+<% end %>

views/upload.erb

@@ -32,22 +32,4 @@
           </div>
         </form>
 
-        <% if @labels && !@labels.empty? %>
-          <hr class="mt-4">
-          <h5>Saved labels</h5>
-          <div class="list-group">
-            <% @labels.each do |label| %>
-              <div class="list-group-item d-flex justify-content-between align-items-center">
-                <%= label['name'] %>
-                <div class="d-flex gap-2">
-                  <form action="/labels/<%= label['id'] %>/print" method="POST">
-                    <button class="btn btn-sm btn-secondary" type="submit">Print</button>
-                  </form>
-                  <form action="/labels/<%= label['id'] %>/delete" method="POST">
-                    <button class="btn btn-sm btn-outline-danger" type="submit">Delete</button>
-                  </form>
-                </div>
-              </div>
-            <% end %>
-          </div>
-        <% end %>
+        <p class="mt-4"><a href="/labels">See saved labels &rarr;</a></p>