feat(gpui, gpui_widgets): i18n string-table hook + node-graph fit API

- gpui::i18n: minimal string-table override (set_table/tr/clear_table) with
  built-in defaults; effect-stack and viewer strings now go through it so
  hosts can localize widget-baked labels without a full i18n framework.
- gpui_widgets::i18n re-exports the hook (gpui_widgets::i18n::set_table).
- node_graph: GraphViewState::fit_to_rect for fit-window/initial viewports
  (unit tested); NodeGraphView::viewport_size accessor for fit targets.

crates/gpui_widgets/src/i18n.rs

@@ -0,0 +1,31 @@
+//! Localization hook for widget-baked strings.
+//!
+//! Re-exports the [`gpui::i18n`] string-table override API so hosts can
+//! localize the widgets' built-in strings as
+//! `gpui_widgets::i18n::set_table(..)`. See [`gpui::i18n`] for the full
+//! contract: [`tr`] returns the installed override for a key, or the
+//! widget's built-in default when none is set.
+//!
+//! [`tr`]: gpui::i18n::tr
+
+pub use gpui::i18n::*;
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// The hook is a thin re-export: installing a table through the widget
+    /// path is visible to `gpui::i18n::tr` and vice versa.
+    #[test]
+    fn widget_path_shares_the_gpui_table() {
+        clear_table();
+        assert_eq!(tr("viewer.safe_frames", "安全框"), "安全框");
+
+        let mut table = StringTable::new();
+        table.insert("viewer.safe_frames".into(), "Safe Frames".into());
+        set_table(table);
+
+        assert_eq!(gpui::i18n::tr("viewer.safe_frames", "安全框"), "Safe Frames");
+        clear_table();
+    }
+}

crates/gpui_widgets/src/lib.rs

@@ -23,6 +23,7 @@ pub mod color;
 pub mod combo_box;
 pub mod curve_editor;
 pub mod dialog;
+pub mod i18n;
 pub mod keyable;
 pub mod menu;
 pub mod project_explorer;

crates/gpui_widgets/src/viewer/mod.rs

@@ -221,7 +221,7 @@ impl<C: PlaybackClock> Render for ViewerWidget<C> {
                     .items_center()
                     .justify_center()
                     .text_color(colors.disabled)
-                    .child("No frame source"),
+                    .child(crate::i18n::tr("viewer.no_frame_source", "No frame source")),
             );
         }
 
@@ -326,7 +326,7 @@ impl<C: PlaybackClock> Render for ViewerWidget<C> {
             )
             .child(button(
                 "gpui-widgets-viewer-safe",
-                "安全框",
+                crate::i18n::tr("viewer.safe_frames", "安全框"),
                 cx.listener(|this, _event: &ClickEvent, _window, cx| {
                     this.show_safe_frames = !this.show_safe_frames;
                     this.emit(
@@ -337,7 +337,7 @@ impl<C: PlaybackClock> Render for ViewerWidget<C> {
             ))
             .child(button(
                 "gpui-widgets-viewer-zoom",
-                "缩放",
+                crate::i18n::tr("viewer.zoom", "缩放"),
                 cx.listener(|this, _event: &ClickEvent, _window, cx| {
                     this.zoom = !this.zoom;
                     this.emit(ViewerEvent::ToggleZoomRequested { control: this.control }, cx);
@@ -351,7 +351,7 @@ impl<C: PlaybackClock> Render for ViewerWidget<C> {
 /// A small labeled button.
 fn button(
     id: &'static str,
-    label: &'static str,
+    label: impl IntoElement,
     on_click: impl Fn(&ClickEvent, &mut Window, &mut App) + 'static,
 ) -> impl IntoElement {
     div()