Fix postcode search layout and placeholder styling

- Keep postcode controls on one line (flex-wrap: nowrap)
- Remove uppercase transform from placeholder text
- Update placeholder to "Enter postcode..." for consistency

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/index.html

@@ -84,7 +84,7 @@
 
                 <div id="location-search-panel" class="search-panel">
                     <div class="location-input-group">
-                        <input type="text" id="postcode-search" class="search-input postcode-input" placeholder="Postcode">
+                        <input type="text" id="postcode-search" class="search-input postcode-input" placeholder="Enter postcode...">
                         <select id="radius-select" class="filter-select radius-select">
                             <option value="1">1 mile</option>
                             <option value="2">2 miles</option>