chore(theme): 同步 YschTheme 再生产物 theme.ts（版本戳 20260923-1454-9619fbf）

仅版本戳注释行变化，正文与 20260921-1219-bb1637c 版一致；main 此前无该文件，本次新增。

src/utils/theme.ts

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+/**
+ * 本文件由 YschTheme scripts/gen-theme.mjs 从 assets-src/pc/theme-core.js 生成（版本 20260923-1454-9619fbf），勿手改。
+ * 分发方式：YschTheme `npm run sync` 拷进各端 src/utils/theme.ts（与 ThemeSwitcher.vue 配套，MD5 对齐报告）。
+ * 运行时档位类名由 /static/js/yh-theme-init.js 在 <head> 内先行挂好，本模块只负责读写与切换。
+ */
+export type ThemeName = "blue" | "ocean" | "ink" | "violet" | "teal";
+
+/** 定稿默认档：blue + side-deep + grad-on + 侧栏跟随（D1 拍板 deep） */
+export interface ThemeState {
+  theme: ThemeName;
+  /** 侧栏深色（false=浅色档） */
+  sideDeep: boolean;
+  /** 顶栏渐变（联动侧栏竖向渐变） */
+  gradOn: boolean;
+  /** 侧栏颜色跟随顶栏品牌色（false=中性灰 side-plain） */
+  sideFollow: boolean;
+}
+
+interface StorageLike {
+  getItem(k: string): string | null;
+  setItem(k: string, v: string): void;
+}
+
+export const THEME_NAMES: readonly ThemeName[] = ["blue", "ocean", "ink", "violet", "teal"];
+
+export const THEME_STORAGE_KEY = "yh-theme";
+
+export const DEFAULT_THEME_STATE: ThemeState = {
+  theme: "blue",
+  sideDeep: true,
+  gradOn: true,
+  sideFollow: true
+};
+
+/** 宽松解析：任一字段非法/缺失即回退默认档（脏数据不阻塞启动） */
+export function parseThemeState(raw: string | null): ThemeState {
+  if (!raw) return { ...DEFAULT_THEME_STATE };
+  try {
+    const o = JSON.parse(raw);
+    if (!o || typeof o !== "object") return { ...DEFAULT_THEME_STATE };
+    return {
+      theme: THEME_NAMES.includes(o.theme) ? o.theme : DEFAULT_THEME_STATE.theme,
+      sideDeep: typeof o.sideDeep === "boolean" ? o.sideDeep : DEFAULT_THEME_STATE.sideDeep,
+      gradOn: typeof o.gradOn === "boolean" ? o.gradOn : DEFAULT_THEME_STATE.gradOn,
+      sideFollow: typeof o.sideFollow === "boolean" ? o.sideFollow : DEFAULT_THEME_STATE.sideFollow
+    };
+  } catch {
+    return { ...DEFAULT_THEME_STATE };
+  }
+}
+
+export function loadThemeState(storage: StorageLike | undefined = globalThis.localStorage): ThemeState {
+  if (!storage) return { ...DEFAULT_THEME_STATE };
+  return parseThemeState(storage.getItem(THEME_STORAGE_KEY));
+}
+
+export function saveThemeState(state: ThemeState, storage: StorageLike | undefined = globalThis.localStorage): void {
+  try {
+    storage?.setItem(THEME_STORAGE_KEY, JSON.stringify(state));
+  } catch {
+    /* 隐私模式/配额失败静默：仅丢持久化，不丢本次会话生效 */
+  }
+}
+
+/** 把状态落到根元素档位类名（幂等：先清后挂），返回传入的 state 便于链式 */
+export function applyThemeState(state: ThemeState, root: HTMLElement = document.documentElement): ThemeState {
+  root.dataset.theme = state.theme;
+  root.classList.toggle("side-deep", state.sideDeep);
+  root.classList.toggle("side-light", !state.sideDeep);
+  root.classList.toggle("grad-on", state.gradOn);
+  root.classList.toggle("grad-off", !state.gradOn);
+  root.classList.toggle("side-plain", !state.sideFollow);
+  return state;
+}
+
+/** 启动引导：各端 main.ts（或本仓 init 脚本的启动段）于挂载前调用，消除首帧闪色 */
+export function initTheme(): ThemeState {
+  return applyThemeState(loadThemeState());
+}