Fix {{Tadvise_test_list}} to always populate from rx_investigations

Previous implementation only built test list when investigation textarea
was empty, preventing {{Tadvise_test_list}} from showing when textarea
had content.

Changes:
- Separated test list building from textarea population logic
- {{Tadvise_test_list}} now always populates when rx_investigations exists
- {{investigation}} still gets comma-separated fallback when textarea empty
- Both placeholders now work independently

Test list HTML output format:
<ul style="margin:3px 0 0 16px;padding:0;list-style-type:disc;">
  <li>CBC (Complete Blood Count)</li>
  <li>ECG (Electrocardiogram)</li>
  <li>HBA1C</li>
</ul>

app/Controllers/Opd.php

@@ -2796,20 +2796,24 @@ class Opd extends BaseController
         };
 
         $rxInvestigation = $rxRead($rx, ['investigation', 'Investigations', 'investigations', 'Investigation']);
+        
+        // Build test list independently from textarea content
         $rxInvestigationTestList = '';
-        if ($rxInvestigation === '' && !empty($data['rx_investigations']) && is_array($data['rx_investigations'])) {
+        if (!empty($data['rx_investigations']) && is_array($data['rx_investigations'])) {
-            $parts = [];
             $testNames = [];
             foreach ($data['rx_investigations'] as $inv) {
                 $txt = trim((string) ($inv['investigation_name'] ?? $inv['investigation'] ?? ''));
                 if ($txt !== '') {
-                    $parts[] = $txt;
                     $testNames[] = $txt;
                 }
             }
-            $rxInvestigation = implode(', ', $parts);
             
-            // Build formatted test list for {{Tadvise_test_list}} placeholder
+            // If textarea is empty, also populate it with comma-separated tests
+            if ($rxInvestigation === '' && !empty($testNames)) {
+                $rxInvestigation = implode(', ', $testNames);
+            }
+            
+            // Always build formatted HTML test list for {{Tadvise_test_list}} placeholder
             if (!empty($testNames)) {
                 $rxInvestigationTestList = '<ul style="margin:3px 0 0 16px;padding:0;list-style-type:disc;">';
                 foreach ($testNames as $testName) {