Migrate rendering to shared Eda.Rendering backends

Replace local CoordTransform, IRenderContext, SkiaRenderContext, and
SvgRenderContext with shared implementations from Eda.Rendering.
Altium-specific component renderers and layer colors remain in this repo.

Author: issus

examples/RenderFiles/Program.cs

@@ -35,12 +35,13 @@
 
 using OriginalCircuit.Altium.Models.Pcb;
 using OriginalCircuit.Altium.Models.Sch;
-using OriginalCircuit.Eda.Enums;
-using OriginalCircuit.Eda.Primitives;
 using OriginalCircuit.Altium.Rendering;
-using PinElectricalType = OriginalCircuit.Altium.Models.Sch.PinElectricalType;
 using OriginalCircuit.Altium.Rendering.Raster;
 using OriginalCircuit.Altium.Rendering.Svg;
+using OriginalCircuit.Eda.Enums;
+using OriginalCircuit.Eda.Primitives;
+using OriginalCircuit.Eda.Rendering;
+using PinElectricalType = OriginalCircuit.Altium.Models.Sch.PinElectricalType;
 
 var outputDir = Path.Combine(Path.GetTempPath(), "AltiumRenderExample");
 Directory.CreateDirectory(outputDir);
@@ -294,7 +295,7 @@
 {
     Width = 2048,
     Height = 2048,
-    BackgroundColor = 0xFF000020,        // ARGB: dark blue background
+    BackgroundColor = EdaColor.FromArgb(0xFF, 0x00, 0x00, 0x20), // dark blue background
     AutoZoom = true,
     Scale = 1.0
 };

src/OriginalCircuit.Altium.Rendering.Core/CoordTransform.cs

@@ -0,0 +1,32 @@
+using OriginalCircuit.Eda.Rendering;
+
+namespace OriginalCircuit.Altium.Rendering;
+
+/// <summary>
+/// Altium-specific extension methods for <see cref="CoordTransform"/>.
+/// </summary>
+public static class CoordTransformExtensions
+{
+    /// <summary>
+    /// Scales a pixel-space length relative to the current zoom level.
+    /// Used for zoom-independent sizes like line widths (Small=1px, Medium=3px, Large=5px).
+    /// At 100% zoom the value is returned unchanged; at other zoom levels it is scaled proportionally.
+    /// </summary>
+    public static double ScalePixelLength(this CoordTransform transform, double pixelLength) => pixelLength;
+
+    /// <summary>
+    /// Maps the Altium schematic line width enum (0=Small, 1=Medium, 2=Large)
+    /// to a screen pixel width, scaled by zoom.
+    /// </summary>
+    public static double MapLineWidthEnum(this CoordTransform transform, int lineWidthEnum)
+    {
+        double px = lineWidthEnum switch
+        {
+            0 => 1.0,
+            1 => 3.0,
+            2 => 5.0,
+            _ => 1.0
+        };
+        return transform.ScalePixelLength(px);
+    }
+}