Add dismiss functionality for cloud-init build status</message>

<message>Implement a new API endpoint to clear the build status to idle, allowing users to dismiss messages after a build is cancelled, completed, or errored. Update the dashboard UI to include a dismiss link that appears under relevant conditions, enhancing user experience by providing a clearer interface for managing build statuses. Modify the JavaScript to handle the dismissal action and ensure proper status updates are reflected in the UI.

emmc-provisioning/dashboard/app.py

@@ -1629,6 +1629,18 @@ def api_build_cloudinit_cancel():
         return jsonify({"ok": False, "error": str(e)}), 500
 
 
+@app.route("/api/build-cloudinit-status-clear", methods=["POST"])
+@require_admin
+def api_build_cloudinit_status_clear():
+    """Clear build status to idle (so message is cleared after cancel/done/error)."""
+    st = _build_status_read()
+    busy = st.get("phase") in ("downloading", "decompressing", "injecting", "finalizing", "resolving")
+    if busy:
+        return jsonify({"ok": False, "error": "Cannot clear while build is in progress"}), 409
+    _build_status_write("idle", "", None, None)
+    return jsonify({"ok": True})
+
+
 @app.route("/api/build-cloudinit", methods=["POST"])
 @require_admin
 def api_build_cloudinit():