refactor: 资源按 游戏/壁纸 分层，预设拆进各自壁纸目录

- assets/<游戏>/<壁纸>/{effects,images,audios}/，每档壁纸自包含
- 每档壁纸自带 preset.js：用 import.meta.url 推导自身资源路径，目录可整体搬走；
  目录名用显示名（含「」），代码键用稳定 id（xilian/kv37，与 WE 属性值绑定）
- preset-store.js -> presets.js：静态 import 两份预设并建 id 索引
- 新增 CONTEXT.md 术语表与 ADR-0001/0002
- 新增 check-paths / compare / heatmap 三个验证工具；serve.mjs 改为每帧强制动画相位归零

验证：check-paths 11/11 路径存在（含此前零引用的 昔涟.flac）；浏览器 0 个真实 404；
与基线 worktree 同冻结设置对拍，9 对跨版本比较中 4 对逐像素完全相同（差异 0），
其余 ≤0.19/255，远低于基线自身的双模态抖动（2.27/255）。

tools/compare.mjs

@@ -0,0 +1,58 @@
+// 对拍比较：把两批截图逐对做差值，给出"改完到底有没有动到画面"的判定。
+// 用法：node tools/compare.mjs <A目录> <B目录> [--tag A] [--tag B] [--threshold 1.0]
+// 例：  node tools/compare.mjs before after
+
+import { spawn } from "node:child_process";
+import { readdir } from "node:fs/promises";
+import { resolve } from "node:path";
+
+const argv = process.argv.slice(2);
+const [dirA, dirB] = argv;
+if (!dirA || !dirB) {
+  console.error("usage: node tools/compare.mjs <dirA> <dirB> [--threshold 1.0]");
+  process.exit(2);
+}
+const opt = (name, dflt) => {
+  const i = argv.indexOf(`--${name}`);
+  return i >= 0 ? argv[i + 1] : dflt;
+};
+const threshold = Number(opt("threshold", "1.0"));
+
+function run(cmd, args) {
+  return new Promise((resolve) => {
+    const p = spawn(cmd, args, { stdio: ["ignore", "pipe", "pipe"] });
+    let out = "";
+    p.stdout.on("data", (d) => (out += d));
+    p.stderr.on("data", (d) => (out += d));
+    p.on("close", () => resolve(out));
+  });
+}
+
+const A = resolve("tools/shots", dirA);
+const B = resolve("tools/shots", dirB);
+const files = (await readdir(A)).filter((f) => f.endsWith(".png") && !f.endsWith(".ref.png")).sort();
+
+let worst = 0;
+let worstName = "";
+let failed = 0;
+
+for (const f of files) {
+  const a = resolve(A, f);
+  const b = resolve(B, f);
+  const out = await run(process.execPath, ["tools/diff.mjs", a, b]);
+  const m = out.match(/mean\|diff\|=([\d.]+)/);
+  const mean = m ? Number(m[1]) : NaN;
+  const verdict = Number.isNaN(mean) ? "MISSING" : mean < threshold ? "same" : "CHANGED";
+  if (Number.isNaN(mean)) failed++;
+  else if (mean > worst) {
+    worst = mean;
+    worstName = f;
+  }
+  console.log(`${f.padEnd(28)} mean|diff|=${String(mean).padStart(7)}   ${verdict}`);
+}
+
+console.log(`\n${dirA} → ${dirB}：${files.length} 对；最大差异 ${worst.toFixed(3)}/255（${worstName || "无"}）；判定阈值 ${threshold}`);
+if (failed) {
+  console.log(`${failed} 对缺少对照文件`);
+  process.exit(1);
+}