chore(frontend): shadcn-svelte / Tailwind / layerchart 工具链初始化

[变更性质]
本轮为维护性依赖与配置初始化，不改变业务页面（页面迁移见后续提交）。

[维护内容]
按 Leader 返工指令，前端 UI 组件库全量迁移 shadcn-svelte，图表渲染
从 echarts 换为 layerchart，需要一次性引入配套依赖与构建配置。

[实现方案]
package.json/pnpm-lock.yaml：tailwindcss@4、@tailwindcss/vite、
tw-animate-css、shadcn-svelte、bits-ui、tailwind-variants、clsx、
tailwind-merge、@lucide/svelte、layerchart、@fontsource-variable/inter
与 @types/node；echarts 保留至页面迁移完成后移除。pnpm-workspace.yaml
声明 allowBuilds（esbuild、@tailwindcss/oxide）。components.json 采用
mira preset，别名 $lib。tsconfig 新增 $lib paths；vite.config.ts 加入
tailwindcss 插件、$lib alias（vitest 需要）与 test 环境配置。
src/lib/components/ 为 shadcn 生成的 UI 组件源码（button/input/label/
card/badge/alert/select/table/tabs/separator/chart），src/lib/utils.ts
为 cn 工具。app.css 引入 tailwind 与 shadcn CSS 变量并调整为 teal
主题（primary #0f766e、radius 0.375rem、双主题 chart-1..5），保留
legacy 选择器（banner/beat/table.data/metric 等），mobileCss.test.ts
依赖其语义断言。

[影响范围]
构建链与主题变量；后续页面提交逐步消费这些组件，npm run check/test/
build 已全绿验证。

1 files changed, 68 insertions, 0 deletions

diff --git a/frontend/src/lib/components/ui/chart/chart-utils.ts b/frontend/src/lib/components/ui/chart/chart-utils.ts
new file mode 100644
index 0000000..6e1f000
--- /dev/null
+++ b/frontend/src/lib/components/ui/chart/chart-utils.ts
@@ -0,0 +1,68 @@
+import { getContext, setContext, type Component, type Snippet } from "svelte";
+import type { Tooltip } from "layerchart";
+
+export const THEMES = { light: "", dark: ".dark" } as const;
+
+export type ChartConfig = {
+	[k in string]: {
+		label?: string;
+		icon?: Component;
+	} & (
+		| { color?: string; theme?: never }
+		| { color?: never; theme: Record<keyof typeof THEMES, string> }
+	);
+};
+
+export type ExtractSnippetParams<T> = T extends Snippet<[infer P]> ? P : never;
+
+export type TooltipPayload = Tooltip.TooltipSeries;
+
+// Helper to extract item config from a payload.
+export function getPayloadConfigFromPayload(
+	config: ChartConfig,
+	payload: TooltipPayload,
+	key: string,
+	// eslint-disable-next-line @typescript-eslint/no-explicit-any
+	data?: Record<string, any> | null
+) {
+	if (typeof payload !== "object" || payload === null) return undefined;
+
+	const payloadConfig =
+		"config" in payload && typeof payload.config === "object" && payload.config !== null
+			? payload.config
+			: undefined;
+
+	let configLabelKey: string = key;
+
+	if (payload.key === key) {
+		configLabelKey = payload.key;
+	} else if (payload.label === key) {
+		configLabelKey = payload.label;
+	} else if (key in payload && typeof payload[key as keyof typeof payload] === "string") {
+		configLabelKey = payload[key as keyof typeof payload] as string;
+	} else if (
+		payloadConfig !== undefined &&
+		key in payloadConfig &&
+		typeof payloadConfig[key as keyof typeof payloadConfig] === "string"
+	) {
+		configLabelKey = payloadConfig[key as keyof typeof payloadConfig] as string;
+	} else if (data != null && key in data && typeof data[key] === "string") {
+		configLabelKey = data[key] as string;
+	}
+
+	return configLabelKey in config ? config[configLabelKey] : config[key as keyof typeof config];
+}
+
+type ChartContextValue = {
+	config: ChartConfig;
+};
+
+const chartContextKey = Symbol("chart-context");
+
+export function setChartContext(value: ChartContextValue) {
+	return setContext(chartContextKey, value);
+}
+
+export function useChart() {
+	return getContext<ChartContextValue>(chartContextKey);
+}