Web: show the brush preset storage banner only while a change is unsaved (#4918)

When the browser denies IndexedDB from the start (a sandboxed iframe without
allow-same-origin, blocked site data), the banner "Brush preset changes are not
saved: SecurityError … Browser storage is unavailable" stays above the app for
the whole session, before any preset was touched and with nothing to dismiss.

Show it only while a preset change is unsaved. Nothing is lost before the first
change; that change brings the same banner with the reason. Write errors and
rejected records keep showing it, as both leave changes unsaved.

Co-authored-by: kuvshin888 <[email protected]>

apps/photocraft-web/src/preset_bridge.rs

@@ -337,6 +337,7 @@ mod tests {
         let b = Bridge::default();
         b.unavailable("SecurityError".into());
         let (mut s, _) = session(b.clone());
+        assert!(!b.unsaved(), "nothing is lost before the first change, so the web shell shows no banner");
         import(&mut s);
         assert!(s.tools.presets.iter().any(|p| p.name == "Browser seam brush"));
         assert!(b.unsaved());

apps/photocraft-web/src/web.rs

@@ -305,7 +305,12 @@ impl eframe::App for WebShell {
     }
 
     fn ui(&mut self, ui: &mut egui::Ui, frame: &mut eframe::Frame) {
-        if let Some(error) = self.presets.error() {
+        // Only while a preset change is unsaved. Storage the browser denies from the start (a
+        // sandboxed iframe, blocked site data) loses nothing until the first change, and that
+        // change brings the banner with the reason.
+        if self.presets.unsaved()
+            && let Some(error) = self.presets.error()
+        {
             egui::Panel::top("browser_preset_storage").show(ui, |ui| {
                 let tokens = photocraft_ui_egui::theme::Tokens::for_kind(self.app.ui.theme);
                 // Put retry first so floating brush windows cannot cover the control.