Recreate Next.js source — shadcn components, chart, types, hooks

Source files were untracked and lost during reset. Recreated:
- page.tsx (full 3-tab dashboard), layout.tsx, globals.css (shadcn theme)
- types.ts, api.ts, utils.ts
- strategy-card.tsx, equity-chart.tsx, positions-panel.tsx
- ui/ (7 shadcn wrappers: card, badge, button, table, tabs, sheet, collapsible, select)
- Config files: next.config.ts, tsconfig.json, postcss.config.mjs, components.json

dashboard-next/postcss.config.mjs

@@ -0,0 +1,6 @@
+const config = {
+  plugins: {
+    "@tailwindcss/postcss": {},
+  },
+};
+export default config;