Restyle the web UI as a dark trading terminal

- Single palette (web/src/styles/palette.ts) taken from the Stitch
  design, exposed as ap-* UnoCSS colors and --ap-* CSS variables and
  used for Element Plus dark theme overrides, KLineChart and the news
  iframe; zero radius, JetBrains Mono / Space Grotesk bundled locally
- New sidebar and header layout; trading page, plan card and analysis
  drawer follow the design; other pages use the same panels
- Status API reports today's closed trades, wins and net PnL, shown as
  today's PnL and win rate on the trading page

web/index.html

@@ -1,5 +1,5 @@
 <!doctype html>
-<html lang="zh-CN">
+<html lang="zh-CN" class="dark">
   <head>
     <meta charset="UTF-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />