feat: implement export functionality for projects and scenarios with CSV and Excel support

templates/partials/import_upload.html

@@ -0,0 +1,25 @@
+{% from "partials/components.html" import feedback %}
+
+<section class="import-upload" data-import-upload>
+  <header class="import-upload__header">
+    <h3>{{ title or "Bulk Import" }}</h3>
+    {% if description %}<p class="import-upload__description">{{ description }}</p>{% endif %}
+  </header>
+
+  <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">
+      Browse
+      <input type="file" name="import-file" accept=".csv,.xlsx" hidden />
+    </label>
+    <p class="import-upload__hint">Maximum size {{ max_size_hint or "10 MB" }}. UTF-8 encoding required.</p>
+  </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>
+  </div>
+
+  {{ feedback("import-upload-feedback", hidden=True, role="alert") }}
+</section>