feat: add star sparkle brush preset and enhance star brush parameters

hcie-iced-app/crates/hcie-iced-gui/src/app.rs

@@ -587,6 +587,12 @@ pub struct ToolState {
     pub brush_color_variant: bool,
     /// Magnitude of the per-dab color variation (0.0..1.0).
     pub brush_variant_amount: f32,
+    /// Star brush base rotation angle in radians.
+    pub brush_angle: f32,
+    /// Star brush per-dab size variance (0.0..1.0).
+    pub brush_size_variance: f32,
+    /// Star brush per-dab angle variance (0.0..1.0).
+    pub brush_angle_variance: f32,
     /// True when the brush color should cycle through the hue over stroke distance.
     pub brush_cyclic_color: bool,
     /// Speed of the hue cycle along the stroke (0.01..5.0).
@@ -625,6 +631,9 @@ impl Default for ToolState {
             brush_spacing: 1.0,
             brush_color_variant: false,
             brush_variant_amount: 0.0,
+            brush_angle: 0.0,
+            brush_size_variance: 0.0,
+            brush_angle_variance: 0.0,
             brush_cyclic_color: false,
             brush_cyclic_speed: 0.5,
             last_update_instant: std::time::Instant::now(),
@@ -784,6 +793,9 @@ pub enum Message {
     BrushSpacingChanged(f32),
     BrushColorVariantToggled(bool),
     BrushVariantAmountChanged(f32),
+    BrushAngleChanged(f32),
+    BrushSizeVarianceChanged(f32),
+    BrushAngleVarianceChanged(f32),
     BrushCyclicColorToggled(bool),
     BrushCyclicSpeedChanged(f32),
     BrushImportAbr,
@@ -1323,6 +1335,9 @@ fn build_brush_tip(state: &ToolState) -> BrushTip {
         spacing: state.brush_spacing,
         color_variant: state.brush_color_variant,
         variant_amount: state.brush_variant_amount,
+        angle: state.brush_angle,
+        roundness: state.brush_size_variance,
+        rotation_random: state.brush_angle_variance,
         ..BrushTip::default()
     }
 }
@@ -4976,6 +4991,21 @@ impl HcieIcedApp {
                 self.settings.update_from_tool_state(&self.tool_state);
                 let _ = self.settings.save();
             }
+            Message::BrushAngleChanged(angle) => {
+                self.tool_state.brush_angle = angle;
+                self.settings.update_from_tool_state(&self.tool_state);
+                let _ = self.settings.save();
+            }
+            Message::BrushSizeVarianceChanged(variance) => {
+                self.tool_state.brush_size_variance = variance;
+                self.settings.update_from_tool_state(&self.tool_state);
+                let _ = self.settings.save();
+            }
+            Message::BrushAngleVarianceChanged(variance) => {
+                self.tool_state.brush_angle_variance = variance;
+                self.settings.update_from_tool_state(&self.tool_state);
+                let _ = self.settings.save();
+            }
             Message::BrushCyclicColorToggled(enabled) => {
                 self.tool_state.brush_cyclic_color = enabled;
                 self.documents[self.active_doc]