feat(web): 采用 Notion 设计系统 — 暖色调 + 白色侧边栏 + Inter 字体

引入 Notion 风格的 DESIGN.md 设计系统文件，并全面重构前端 UI：

- 主色从 Indigo (#4F46E5) 迁移到 Notion Blue (#0075de)
- 页面背景从冷灰 (#F1F5F9) 迁移到暖白 (#f6f5f4)
- 侧边栏从深色 (#0F172A) 迁移到白色，活跃项用蓝色指示
- 文字从 Slate 冷色迁移到暖灰系列 (Warm Gray 500/300)
- 圆角从 8px 缩小到 4px（按钮/输入），8px（卡片）
- 阴影改为多层超轻 Notion 风格（最大 opacity 0.05）
- 字体优先使用 Inter，保留中文回退
- 暗色模式适配暖黑色调 (#191918)
- 更新 27 个前端文件的硬编码颜色值

apps/web/src/pages/plugins/graph/graphConstants.ts

@@ -5,11 +5,11 @@
 
 // 通用边调色板
 const EDGE_PALETTE: Array<{ base: string; light: string; glow: string }> = [
-  { base: '#4F46E5', light: '#818CF8', glow: 'rgba(79,70,229,0.3)' },
-  { base: '#059669', light: '#34D399', glow: 'rgba(5,150,105,0.3)' },
-  { base: '#D97706', light: '#FBBF24', glow: 'rgba(217,119,6,0.3)' },
+  { base: '#0075de', light: '#62aef0', glow: 'rgba(79,70,229,0.3)' },
+  { base: '#1aae39', light: '#34D399', glow: 'rgba(5,150,105,0.3)' },
+  { base: '#dd5b00', light: '#FBBF24', glow: 'rgba(217,119,6,0.3)' },
   { base: '#0891B2', light: '#22D3EE', glow: 'rgba(8,145,178,0.3)' },
-  { base: '#DC2626', light: '#F87171', glow: 'rgba(220,38,38,0.3)' },
+  { base: '#e5534b', light: '#F87171', glow: 'rgba(220,38,38,0.3)' },
   { base: '#7C3AED', light: '#A78BFA', glow: 'rgba(124,58,237,0.3)' },
   { base: '#EA580C', light: '#FB923C', glow: 'rgba(234,88,12,0.3)' },
   { base: '#DB2777', light: '#F472B6', glow: 'rgba(219,39,119,0.3)' },

apps/web/src/pages/plugins/graph/graphRenderer.ts

@@ -295,8 +295,8 @@ export function drawFullGraph(
     const degree = degreeMap.get(node.id) || 0;
     const r = degreeToRadius(degree, isCenter);
 
-    let nodeColorBase = '#4F46E5';
-    let nodeColorLight = '#818CF8';
+    let nodeColorBase = '#0075de';
+    let nodeColorLight = '#62aef0';
     let nodeColorGlow = 'rgba(79,70,229,0.3)';
 
     if (isCenter) {