feat: add llm-client.js with prompt builder and JSON extractor

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tests/scene_generator_llm_test.js

@@ -0,0 +1,45 @@
+const assert = require("assert");
+const {
+  buildAnalyzePrompt,
+  extractJsonFromResponse,
+} = require("../frontend/scene-generator/llm-client");
+
+function testBuildAnalyzePromptIncludesFileContents() {
+  const dirContents = {
+    "scene.toml": '[scene]\nid = "test-scene"',
+    scripts: { "collect_test.js": "async function main() {}" },
+    tree: "├── scene.toml\n└── collect_test.js",
+  };
+
+  const prompt = buildAnalyzePrompt("D:/test/scenario", dirContents);
+
+  assert.ok(prompt.includes("scene.toml"), "should include scene.toml");
+  assert.ok(prompt.includes("collect_test.js"), "should include script name");
+  assert.ok(prompt.includes("D:/test/scenario"), "should include sourceDir");
+  console.log("PASS: testBuildAnalyzePromptIncludesFileContents");
+}
+
+function testExtractJsonFromResponse() {
+  const withMarkdown =
+    '```json\n{"sceneId": "test", "sceneName": "测试"}\n```';
+  const plain = '{"sceneId": "test", "sceneName": "测试"}';
+  const withPrefix =
+    'Here is the result:\n{"sceneId": "test", "sceneName": "测试"}';
+
+  assert.deepStrictEqual(extractJsonFromResponse(withMarkdown), {
+    sceneId: "test",
+    sceneName: "测试",
+  });
+  assert.deepStrictEqual(extractJsonFromResponse(plain), {
+    sceneId: "test",
+    sceneName: "测试",
+  });
+  assert.deepStrictEqual(extractJsonFromResponse(withPrefix), {
+    sceneId: "test",
+    sceneName: "测试",
+  });
+  console.log("PASS: testExtractJsonFromResponse");
+}
+
+testBuildAnalyzePromptIncludesFileContents();
+testExtractJsonFromResponse();