fix: add auto-refresh for processing exports on index page (#715)

Wrap export list in turbo_frame_tag with conditional polling attributes.
When exports are pending/processing, page polls every 3 seconds for updates.
Add turbo_frame: _top to download/delete buttons for proper frame handling.

app/javascript/controllers/polling_controller.js

@@ -0,0 +1,64 @@
+import { Controller } from "@hotwired/stimulus";
+
+// Connects to data-controller="polling"
+// Automatically refreshes a turbo frame at a specified interval
+export default class extends Controller {
+  static values = {
+    url: String,
+    interval: { type: Number, default: 3000 },
+  };
+
+  connect() {
+    this.startPolling();
+  }
+
+  disconnect() {
+    this.stopPolling();
+  }
+
+  startPolling() {
+    if (!this.hasUrlValue) return;
+
+    this.poll = setInterval(() => {
+      this.refresh();
+    }, this.intervalValue);
+  }
+
+  stopPolling() {
+    if (this.poll) {
+      clearInterval(this.poll);
+      this.poll = null;
+    }
+  }
+
+  async refresh() {
+    try {
+      const response = await fetch(this.urlValue, {
+        headers: {
+          Accept: "text/vnd.turbo-stream.html",
+          "Turbo-Frame": this.element.id,
+        },
+      });
+
+      if (response.ok) {
+        const html = await response.text();
+        const template = document.createElement("template");
+        template.innerHTML = html;
+
+        const newFrame = template.content.querySelector(
+          `turbo-frame#${this.element.id}`,
+        );
+        if (newFrame) {
+          this.element.innerHTML = newFrame.innerHTML;
+
+          // Check if we should stop polling (no more pending/processing exports)
+          if (!newFrame.hasAttribute("data-polling-url-value")) {
+            this.stopPolling();
+          }
+        }
+      }
+    } catch (error) {
+      console.error("Polling error:", error);
+    }
+  }
+}