[App] Add onboarding wizard (#7064)

* [App] Add onboarding wizard

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* Adjust CI

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* Adjust CI again

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* Comments and fixes

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* Rebase.

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* Comments.

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* CI lol

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* CI again lol

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* Drop some settings, add some new ones.

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* Resize when expanding section

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Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>

cockatrice/src/interface/widgets/onboarding/shader_banner_widget.h

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+#ifndef SHADER_BANNER_WIDGET_H
+#define SHADER_BANNER_WIDGET_H
+
+#include <QElapsedTimer>
+#include <QTimer>
+#include <QWidget>
+
+class BannerShaderConfig;
+class QQuickWidget;
+class GradientFallbackWidget;
+class QStackedLayout;
+
+/** @brief Onboarding banner: a subtle, looping brand-shader animation, one of six
+ *         per-page "motifs" driving the same prebaked fragment shader
+ *         (onboarding/shaders/brand_banner.frag) with different uniform values, so
+ *         every page feels distinct but unmistakably part of the same family.
+ *
+ * Motif switches crossfade smoothly (see BrandBanner.qml's two stacked
+ * ShaderEffect layers + Behavior on opacity) rather than cutting instantly
+ * -- BannerHost just writes the new preset into whichever layer is
+ * currently hidden and flips BannerShaderConfig::frontIsA; QML handles the
+ * actual animation declaratively.
+ *
+ * Falls back to a static two-stop gradient (no shader, no QQuickWidget) if
+ * the platform's Qt Quick scenegraph can't initialize -- e.g. software
+ * rendering only, or a CI/VM environment with no GPU -- so onboarding
+ * never blocks or blanks out over a graphics driver problem. The fallback
+ * is permanent for the lifetime of this widget once triggered. */
+class BannerHost : public QWidget
+{
+    Q_OBJECT
+
+public:
+    enum class Motif
+    {
+        Welcome,
+        CardDatabase,
+        Theming,
+        Account,
+        Preferences,
+        Finish,
+    };
+
+    explicit BannerHost(QWidget *parent = nullptr);
+
+    void setMotif(Motif motif);
+
+protected:
+    void showEvent(QShowEvent *event) override;
+    void hideEvent(QHideEvent *event) override;
+    void resizeEvent(QResizeEvent *event) override;
+
+private slots:
+    void tick();
+    void onSceneGraphFailed();
+
+private:
+    struct Preset
+    {
+        qreal mode;
+        qreal speed;
+        qreal seed;
+    };
+
+    static Preset presetFor(Motif motif);
+
+    void applyMotifPreset(Motif motif);
+    void updateAspect();
+    void activateFallback();
+
+    QStackedLayout *stack;
+    QQuickWidget *quickWidget = nullptr;
+    BannerShaderConfig *config = nullptr;
+    GradientFallbackWidget *fallback = nullptr;
+
+    QTimer clock;
+    QElapsedTimer elapsed;
+    Motif currentMotif = Motif::Welcome;
+    bool usingFallback = false;
+    bool isFirstApply = true;
+};
+
+#endif // SHADER_BANNER_WIDGET_H