feat(web): B4 枚举标签映射 — labelFor 未知值原样显示

- 新增 lib/enums.ts：platform/mood 标签 + labelFor(kind,value)，未知值原样返回（display-raw 红线），注释标明权威来源是 GET /api/v1/meta/enums
- 4 处 mood 渲染改用标签（Nav/TopBar/chat×2）；未动 types.ts 的 MODES/Mode
- 新增纯逻辑测试 enums.test.ts（47 项，esbuild+node，零新依赖）
- 未动 admin channelFields 的第二份 PLATFORM_LABEL（记入待办）

frontend/web/src/components/TopBar.tsx

@@ -3,6 +3,7 @@ import { useAppStore } from "../store/useAppStore";
 import { useModeStore } from "../store/useModeStore";
 import { applyTheme, readTheme, type ThemeMode } from "../lib/theme";
 import { personaAvatar } from "../lib/persona";
+import { labelFor } from "../lib/enums";
 import type { Mode, WsStatus } from "../lib/types";
 import { Tag } from "./primitives";
 import { Icon, type IconName } from "./Icon";
@@ -67,7 +68,7 @@ export function TopBar({ onMenu }: { onMenu: () => void }): React.ReactNode {
 
       <div className="flex-1" />
 
-      {mood ? <Tag tone="accent" className="hidden sm:inline-flex">心情 · {mood}</Tag> : null}
+      {mood ? <Tag tone="accent" className="hidden sm:inline-flex">心情 · {labelFor("mood", mood)}</Tag> : null}
 
       <AwakenBadge />