feat: add embedded GLTF primitives for basic shapes with caching support

bridge/src/primitives.rs

@@ -0,0 +1,41 @@
+use std::path::PathBuf;
+use std::fs;
+
+// Embedded GLTF primitives for basic shapes
+pub mod embedded_models {
+    use super::*;
+    use std::sync::OnceLock;
+    
+    static CACHE_DIR: OnceLock<PathBuf> = OnceLock::new();
+    
+    pub fn get_cache_dir() -> &'static PathBuf {
+        CACHE_DIR.get_or_init(|| {
+            let dir = dirs::cache_dir()
+                .unwrap_or_else(|| PathBuf::from("/tmp"))
+                .join("starworld/primitives");
+            let _ = std::fs::create_dir_all(&dir);
+            dir
+        })
+    }
+    
+    pub fn get_cube_model() -> PathBuf {
+        let path = get_cache_dir().join("cube.glb");
+        if !path.exists() {
+            std::fs::write(&path, CUBE_GLB).expect("Failed to write cube.glb");
+        }
+        path
+    }
+    
+    pub fn get_sphere_model() -> PathBuf {
+        let path = get_cache_dir().join("sphere.glb");
+        if !path.exists() {
+            std::fs::write(&path, SPHERE_GLB).expect("Failed to write sphere.glb");
+        }
+        path
+    }
+    
+    // Minimal cube GLB (binary GLTF) - this is a placeholder
+    // TODO: Generate proper GLB data or bundle actual primitive files
+    const CUBE_GLB: &[u8] = b""; // Will be filled with actual data
+    const SPHERE_GLB: &[u8] = b""; // Will be filled with actual data
+}