feat: introduce SVG-based complex vector shapes

- Added `SvgShape` variant to `VectorShape` in `hcie-protocol`, allowing for SVG rendering of complex shapes.
- Updated serialization to skip old shape variants for backward compatibility.
- Implemented SVG generation functions in `svg_templates.rs` for various shapes (arrow, star, rhombus, etc.).
- Created `svg_render.rs` to parse SVG strings and tessellate paths using `usvg`.
- Modified rendering logic in `hcie-vector` to handle `SvgShape` and integrate with existing shape rendering.
- Updated shape creation API in `hcie-engine-api` to support SVG shapes.
- Enhanced property editing and shape synchronization in both `hcie-egui-app` and `hcie-iced-app` to accommodate new SVG shapes.
- Added comprehensive documentation for new features and changes.

hcie-engine-api/src/lib.rs

@@ -415,6 +415,39 @@ pub struct Engine {
         std::sync::Arc<std::sync::Mutex<Vec<crate::stroke_cache::PendingHistoryItem>>>,
 }
 
+/// Create a `VectorShape::SvgShape` from a shape kind name and parameter map.
+///
+/// The `kind` string must be one of: "arrow", "star", "rhombus", "cylinder",
+/// "heart", "bubble", "gear", "cross", "crescent", "bolt", "arrow4".
+///
+/// Shape-specific parameters (e.g. `points`, `inner_radius`, `thick`) are passed
+/// via `params`.
+pub fn create_vector_shape(
+    kind: &str,
+    x1: f32,
+    y1: f32,
+    x2: f32,
+    y2: f32,
+    params: &std::collections::HashMap<String, f32>,
+) -> VectorShape {
+    let svg = hcie_vector::svg_templates::create_svg(kind, params);
+    VectorShape::SvgShape {
+        x1,
+        y1,
+        x2,
+        y2,
+        kind: kind.to_string(),
+        svg,
+        stroke: 2.0,
+        color: [0, 0, 0, 255],
+        fill_color: [255, 255, 255, 255],
+        fill: true,
+        angle: 0.0,
+        opacity: 1.0,
+        hardness: 1.0,
+    }
+}
+
 impl Engine {
     /// Create a new engine with a default transparent document.
     ///
@@ -4038,6 +4071,14 @@ fn set_shape_color(
             *color = stroke_color;
             *fc = fill_color;
         }
+        SvgShape {
+            color,
+            fill_color: fc,
+            ..
+        } => {
+            *color = stroke_color;
+            *fc = fill_color;
+        }
         FreePath {
             color,
             fill_color: fc,
@@ -4147,6 +4188,12 @@ fn move_shape(
             *x2 += dx;
             *y2 += dy;
         }
+        SvgShape { x1, y1, x2, y2, .. } => {
+            *x1 += dx;
+            *y1 += dy;
+            *x2 += dx;
+            *y2 += dy;
+        }
         FreePath { pts, .. } => {
             for p in pts.iter_mut() {
                 p[0] += dx;
@@ -4279,6 +4326,14 @@ fn scale_shape(shape: &mut hcie_protocol::VectorShape, scale_x: f32, scale_y: f3
             *x2 = cx + (*x2 - cx) * scale_x;
             *y2 = cy + (*y2 - cy) * scale_y;
         }
+        SvgShape { x1, y1, x2, y2, .. } => {
+            let cx = (*x1 + *x2) / 2.0;
+            let cy = (*y1 + *y2) / 2.0;
+            *x1 = cx + (*x1 - cx) * scale_x;
+            *y1 = cy + (*y1 - cy) * scale_y;
+            *x2 = cx + (*x2 - cx) * scale_x;
+            *y2 = cy + (*y2 - cy) * scale_y;
+        }
         FreePath { pts, .. } => {
             if pts.is_empty() {
                 return;