message_move: Disable stream select dropdown for unprivileged users.

This commit disables the stream-select dropdown in the "Move message"
modal if the user is not allowed to move messages between streams, and
adds a tooltip for clarification when the dropdown is disabled.

 Fixes #28345.

web/src/stream_popover.js

@@ -555,6 +555,9 @@ export async function build_move_topic_to_stream_popover(
 
         render_selected_stream();
         $("#move_topic_to_stream_widget").prop("disabled", disable_stream_input);
+        if (disable_stream_input) {
+            $stream_header_colorblock.addClass("disabled");
+        }
         $("#move_topic_modal .move_messages_edit_topic").on("input", () => {
             update_submit_button_disabled_state(stream_widget_value);
         });

web/src/tippyjs.ts

@@ -520,4 +520,21 @@ export function initialize(): void {
         placement: "bottom",
         appendTo: () => document.body,
     });
+
+    delegate("body", {
+        target: "#move_topic_to_stream_widget_wrapper",
+        onShow(instance) {
+            if ($("#move_topic_to_stream_widget").prop("disabled")) {
+                instance.setContent(
+                    $t({
+                        defaultMessage:
+                            "You do not have permission to move messages to another stream in this organization.",
+                    }),
+                );
+                return undefined;
+            }
+            return false;
+        },
+        appendTo: () => document.body,
+    });
 }

web/styles/dark_theme.css

@@ -378,6 +378,10 @@
         }
     }
 
+    .stream_header_colorblock.disabled {
+        filter: brightness(50%);
+    }
+
     /* this one is because in the app we have blue and in dark-theme it should be white. */
     .popover a {
         color: inherit;