feat: update workspace paths and enhance gitignore

- Updated stablediffusion crate path from "../stable-diffusion-burn" to "./crates/stable-diffusion-burn" for proper workspace resolution
- Enhanced .gitignore to include generated model files (.mpk, .pt, .bin, .safetensors, .ckpt) and user_data directory
- Added Cargo.lock to gitignore with appropriate comment
- Reorganized IDE files section in gitignore for better clarity
- Added newline at end of file for proper formatting

crates/stable-diffusion-burn/burn-crates/burn-dispatch/build.rs

@@ -0,0 +1,35 @@
+fn main() {
+    println!("cargo::rustc-check-cfg=cfg(wgpu_metal)");
+    println!("cargo::rustc-check-cfg=cfg(wgpu_vulkan)");
+    println!("cargo::rustc-check-cfg=cfg(wgpu_webgpu)");
+
+    // Detect which single wgpu backend is enabled
+    let metal = cfg!(feature = "metal");
+    let vulkan = cfg!(feature = "vulkan");
+    let webgpu = cfg!(feature = "webgpu");
+    let enabled = [(metal, "metal"), (vulkan, "vulkan"), (webgpu, "webgpu")]
+        .iter()
+        .filter(|x| x.0)
+        .map(|x| x.1)
+        .collect::<Vec<_>>();
+
+    // WGPU features are mutually exclusive, but we don't want to workspace to throw a compile error.
+    // In workspace builds with multiple features, we emit a warning and disable all WGPU backends.
+    if enabled.len() > 1 {
+        println!(
+            "cargo:warning=Only one WGPU backend can be enabled at once. Detected: [{}]. No WGPU backend will be available in this build. This is expected in workspace builds. For production, enable only one of: metal, vulkan, or webgpu.",
+            enabled.join(", ")
+        );
+        return;
+    }
+
+    if metal {
+        println!("cargo:rustc-cfg=wgpu_metal");
+    }
+    if vulkan {
+        println!("cargo:rustc-cfg=wgpu_vulkan");
+    }
+    if webgpu {
+        println!("cargo:rustc-cfg=wgpu_webgpu");
+    }
+}