Add form styles and update button classes for consistency

- Introduced a new CSS file for form styles (forms.css) to enhance form layout and design.
- Removed deprecated button styles from imports.css and updated button classes across templates to use the new utility classes.
- Updated various templates to reflect the new button styles, ensuring a consistent look and feel throughout the application.
- Refactored form-related styles in main.css and removed redundant styles from projects.css and scenarios.css.
- Ensured responsive design adjustments for form actions in smaller viewports.

templates/partials/import_upload.html

@@ -9,7 +9,7 @@
   <div class="import-upload__dropzone" data-import-dropzone>
     <span class="icon-upload" aria-hidden="true"></span>
     <p>Drag & drop CSV/XLSX files here or</p>
-    <label class="btn secondary">
+  <label class="btn btn--secondary">
       Browse
       <input type="file" name="import-file" accept=".csv,.xlsx" hidden />
     </label>
@@ -17,8 +17,8 @@
   </div>
 
   <div class="import-upload__actions">
-    <button type="button" class="btn primary" data-import-upload-trigger disabled>Upload & Preview</button>
-    <button type="button" class="btn" data-import-reset hidden>Reset</button>
+  <button type="button" class="btn btn--primary" data-import-upload-trigger disabled>Upload & Preview</button>
+  <button type="button" class="btn btn--secondary" data-import-reset hidden>Reset</button>
   </div>
 
   {{ feedback("import-upload-feedback", hidden=True, role="alert") }}