feat(qbz-slint): splash screen during session restore

Adds a splash screen (logo, wordmark, spinner) shown while the app
boots and restores a saved session. The login form no longer flashes
for returning users — the app starts on `splash` and resolves to
`shell` (restored) or `login` (no saved session), matching the current
QBZ app behavior.

cc

crates/qbz-slint/src/main.rs

@@ -115,8 +115,14 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
                     log::info!("[qbz-slint] session restored for user {user_id}");
                     enter_shell(runtime, weak, image_cache).await;
                 }
-                Ok(None) => log::info!("[qbz-slint] no saved session — showing login"),
-                Err(e) => log::error!("[qbz-slint] session restore failed: {e}"),
+                Ok(None) => {
+                    log::info!("[qbz-slint] no saved session — showing login");
+                    let _ = weak.upgrade_in_event_loop(|w| w.set_screen(AppScreen::Login));
+                }
+                Err(e) => {
+                    log::error!("[qbz-slint] session restore failed: {e}");
+                    let _ = weak.upgrade_in_event_loop(|w| w.set_screen(AppScreen::Login));
+                }
             }
         });
     }

crates/qbz-slint/ui/app.slint

@@ -5,16 +5,16 @@
 // (POC ADR, sections 13 and 21).
 
 import { Theme } from "foundation/semantic-colors.slint";
+import { SplashScreen } from "splash/SplashScreen.slint";
 import { LoginScreen } from "login/LoginScreen.slint";
 import { AppShell } from "shell/AppShell.slint";
 
 // Re-export the HomeState global so the Rust layer can populate it.
 export { HomeState } from "state.slint";
 
-// Which top-level screen is shown. During M1 the screen switches on a
-// login-button click without real authentication; M2 ties the switch
-// to a real session.
-export enum AppScreen { login, shell }
+// Which top-level screen is shown. The app starts on `splash` while it
+// restores a saved session, then resolves to `shell` or `login`.
+export enum AppScreen { splash, login, shell }
 
 export component AppWindow inherits Window {
     title: "QBZ";
@@ -24,7 +24,7 @@ export component AppWindow inherits Window {
     min-height: 600px;
     background: Theme.surface-main;
 
-    in-out property <AppScreen> screen: AppScreen.login;
+    in-out property <AppScreen> screen: AppScreen.splash;
 
     // Forwarded to the Rust layer, which maps them to typed AppCommands.
     callback sign-in-via-browser();
@@ -32,6 +32,8 @@ export component AppWindow inherits Window {
     callback start-offline();
     callback open-tos();
 
+    if root.screen == AppScreen.splash: SplashScreen { }
+
     if root.screen == AppScreen.login: LoginScreen {
         sign-in-via-browser => {
             root.sign-in-via-browser();

crates/qbz-slint/ui/splash/SplashScreen.slint

@@ -0,0 +1,72 @@
+// Splash screen — shown while the app boots and tries to restore a
+// saved session, so the login form never flashes for returning users.
+
+import { Theme } from "../foundation/semantic-colors.slint";
+import { Typography } from "../foundation/typography.slint";
+import { Radius } from "../foundation/radius.slint";
+import { Spacing } from "../foundation/spacing.slint";
+import { Spinner } from "std-widgets.slint";
+
+export component SplashScreen inherits Rectangle {
+    background: Theme.surface-main;
+
+    VerticalLayout {
+        alignment: center;
+
+        HorizontalLayout {
+            alignment: center;
+
+            Rectangle {
+                width: 720px;
+                background: Theme.surface-card;
+                border-radius: Radius.lg;
+                drop-shadow-blur: 32px;
+                drop-shadow-color: Theme.card-shadow;
+                drop-shadow-offset-y: 8px;
+
+                VerticalLayout {
+                    padding: Spacing.card-padding;
+                    spacing: 0px;
+
+                    HorizontalLayout {
+                        alignment: center;
+                        Image {
+                            source: @image-url("../assets/qbz-logo.png");
+                            width: 140px;
+                            height: 140px;
+                            image-fit: contain;
+                        }
+                    }
+                    Rectangle { height: Spacing.sm; }
+                    Text {
+                        text: @tr("QBZ");
+                        color: Theme.text-primary;
+                        font-size: Typography.wordmark;
+                        font-weight: Typography.semibold;
+                        letter-spacing: 8px;
+                        horizontal-alignment: center;
+                    }
+                    Rectangle { height: 2px; }
+                    Text {
+                        text: @tr("QOBUZ™ PLAYER");
+                        color: Theme.text-muted;
+                        font-size: Typography.subtitle;
+                        letter-spacing: 4px;
+                        horizontal-alignment: center;
+                    }
+
+                    Rectangle { height: Spacing.xl; }
+
+                    HorizontalLayout {
+                        alignment: center;
+                        Spinner {
+                            indeterminate: true;
+                            width: 30px;
+                            height: 30px;
+                        }
+                    }
+                }
+            }
+        }
+    }
+}