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]

frontend/scene-generator/config-loader.js

@@ -0,0 +1,89 @@
+const fs = require("fs");
+const path = require("path");
+
+function resolveProjectRoot() {
+  const envRoot = process.env.SGCLAW_PROJECT_ROOT;
+  if (envRoot && fs.existsSync(envRoot)) {
+    return path.resolve(envRoot);
+  }
+
+  const configPath = resolveConfigPath();
+  if (configPath && fs.existsSync(configPath)) {
+    return path.dirname(configPath);
+  }
+
+  return path.resolve(__dirname);
+}
+
+function resolveConfigPath() {
+  const envPath = process.env.SGCLAW_CONFIG_PATH;
+  if (envPath && fs.existsSync(envPath)) {
+    return path.resolve(envPath);
+  }
+
+  const candidates = [
+    path.resolve(__dirname, "..", "..", "sgclaw_config.json"),
+    path.resolve(__dirname, "..", "sgclaw_config.json"),
+    path.resolve(__dirname, "sgclaw_config.json"),
+  ];
+
+  for (const p of candidates) {
+    if (fs.existsSync(p)) return p;
+  }
+
+  return null;
+}
+
+function loadConfig() {
+  const configPath = resolveConfigPath();
+  if (!configPath) {
+    throw new Error(
+      "sgclaw_config.json not found. Set SGCLAW_CONFIG_PATH or place it in the project root."
+    );
+  }
+
+  const raw = fs.readFileSync(configPath, "utf-8");
+  const config = JSON.parse(raw);
+
+  const apiKey = config.apiKey || "";
+  const baseUrl = config.baseUrl || "";
+  const model = config.model || "";
+
+  if (!apiKey) throw new Error("sgclaw_config.json: 'apiKey' is required");
+  if (!baseUrl) throw new Error("sgclaw_config.json: 'baseUrl' is required");
+  if (!model) throw new Error("sgclaw_config.json: 'model' is required");
+
+  return {
+    apiKey,
+    baseUrl: normalizeBaseUrl(baseUrl),
+    model,
+    projectRoot: resolveProjectRoot(),
+    configPath,
+  };
+}
+
+function normalizeBaseUrl(url) {
+  url = url.replace(/\/+$/, "");
+  if (!url.endsWith("/v1")) url = url + "/v1";
+  return url;
+}
+
+function getDefaults() {
+  const config = loadConfig();
+  const projectRoot = config.projectRoot;
+
+  return {
+    outputRoot: path.join(projectRoot, "examples", "generated_scene_platform"),
+    lessonsPath: path.join(
+      projectRoot,
+      "docs",
+      "superpowers",
+      "references",
+      "tq-lineloss-lessons-learned.toml"
+    ),
+    llmBaseUrl: config.baseUrl,
+    llmModel: config.model,
+  };
+}
+
+module.exports = { loadConfig, getDefaults, resolveProjectRoot, resolveConfigPath };