update step descriptions: remove file format references, rename gene expression CSV label

frontend/index.html

@@ -465,7 +465,7 @@ input[type="range"]::-webkit-slider-thumb {
     <div class="col-card">
       <div class="col-label">Step 1</div>
       <div class="step-title">Prefixed model files</div>
-      <div class="step-desc">One .xlsx per species — output from Step 4 of the Metabolic Community Pipeline.</div>
+      <div class="step-desc">One file per species — output from Step 4 of the Metabolic Community Pipeline.</div>
       <div class="drop-zone" id="dropModel">
         <input type="file" id="fileModel" accept=".xlsx" multiple onchange="handleFiles('model', this.files)"/>
         <span class="drop-icon">📄</span>
@@ -483,7 +483,7 @@ input[type="range"]::-webkit-slider-thumb {
     <div class="col-card">
       <div class="col-label">Step 2</div>
       <div class="step-title">Identifier mapping files</div>
-      <div class="step-desc">One .xlsx per species, in the same order as model files — output from Step 3 of the Pipeline.</div>
+      <div class="step-desc">One file per species, in the same order as model files — output from Step 3 of the Pipeline.</div>
       <div class="drop-zone" id="dropMapping">
         <input type="file" id="fileMapping" accept=".xlsx" multiple onchange="handleFiles('mapping', this.files)"/>
         <span class="drop-icon">📄</span>
@@ -501,7 +501,7 @@ input[type="range"]::-webkit-slider-thumb {
     <!-- Bottom-right: Step 3 -->
     <div class="col-card">
       <div class="col-label">Step 3</div>
-      <div class="step-title">Combined gene expression CSV</div>
+      <div class="step-title">Combined gene expression file</div>
       <div class="step-desc">Normalised gene expression counts for all species and samples from your metatranscriptomics data.</div>
       <div class="drop-zone" id="dropExpr">
         <input type="file" id="fileExpr" accept=".csv" onchange="handleFiles('expr', this.files)"/>