feat: add config-loader.js and initial server test

Add config-loader.js module for loading sgclaw_config.json credentials
and resolving project root directory. Add initial Rust source-guard test
to verify server file paths exist.

🤖 Generated with [Qoder][https://qoder.com]

tests/scene_generator_server_test.rs

@@ -0,0 +1,39 @@
+use std::fs;
+use std::path::PathBuf;
+
+#[test]
+fn scene_generator_server_files_exist() {
+    let manifest_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+    let server_js = manifest_dir
+        .join("frontend")
+        .join("scene-generator")
+        .join("server.js");
+    let config_loader = manifest_dir
+        .join("frontend")
+        .join("scene-generator")
+        .join("config-loader.js");
+
+    assert!(
+        server_js.exists(),
+        "server.js not found at {:?}",
+        server_js
+    );
+    assert!(
+        config_loader.exists(),
+        "config-loader.js not found at {:?}",
+        config_loader
+    );
+}
+
+#[test]
+fn sgclaw_config_is_readable() {
+    let manifest_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+    let config_path = manifest_dir.join("sgclaw_config.json");
+    let content = fs::read_to_string(&config_path)
+        .unwrap_or_else(|err| panic!("sgclaw_config.json not found: {}", err));
+    let parsed: serde_json::Value =
+        serde_json::from_str(&content).expect("should be valid JSON");
+    assert!(parsed.get("apiKey").is_some(), "missing apiKey");
+    assert!(parsed.get("baseUrl").is_some(), "missing baseUrl");
+    assert!(parsed.get("model").is_some(), "missing model");
+}