fix: select only filename (without extension) when renaming files

When renaming a file (e.g. image.png), the input now selects only
'image' instead of 'image.png', preventing accidental extension changes.
Folders still select the full name. Uses setSelectionRange(0, lastDot)
to position cursor selection up to the last dot.

Closes suggestion from issue #83 feedback.

static/js/modal.js

@@ -19,6 +19,9 @@ const Modal = {
     onConfirm: null,
     onCancel: null,
     
+    // Rename mode: select only name without extension
+    _selectNameOnly: false,
+    
     /**
      * Initialize modal system
      */
@@ -141,6 +144,9 @@ const Modal = {
     promptRename(currentName, isFolder = false) {
         const t = window.i18n ? window.i18n.t.bind(window.i18n) : (k) => k;
         
+        // For files, we want to select only the name part (without extension)
+        this._selectNameOnly = !isFolder;
+        
         return this.prompt({
             title: t('dialogs.rename_title') || 'Renombrar',
             label: t('dialogs.new_name') || 'Nuevo nombre',
@@ -168,7 +174,20 @@ const Modal = {
         // Focus input after animation
         setTimeout(() => {
             this.input.focus();
-            this.input.select();
+            
+            if (this._selectNameOnly) {
+                // Select only the filename, excluding the extension
+                const value = this.input.value;
+                const lastDot = value.lastIndexOf('.');
+                if (lastDot > 0) {
+                    this.input.setSelectionRange(0, lastDot);
+                } else {
+                    this.input.select();
+                }
+                this._selectNameOnly = false;
+            } else {
+                this.input.select();
+            }
         }, 100);
     },