feat: implement dark/light mode with system detection

- Install and configure next-themes for theme management
- Add ThemeProvider wrapper component with suppressHydrationWarning
- Define light theme CSS variables (off-white backgrounds, green accents)
- Define dark theme CSS variables (hacker theme: terminal blacks, matrix green)
- Update scrollbar styles for both themes
- Add CRT scanline/glow effects (dark mode only)
- Create ThemeToggle component with system/light/dark cycling
- Add theme toggle to Toolbox sidebar
- Update CandleChart to apply theme-specific colors
- Chart colors update dynamically on theme change
- All components use CSS variables for theme compatibility
- FOUC prevention via next-themes inline script

package-lock.json

@@ -24,6 +24,7 @@
         "lightweight-charts": "^4.2.3",
         "lucide-react": "^0.563.0",
         "next": "^16.1.6",
+        "next-themes": "^0.4.6",
         "papaparse": "^5.5.3",
         "postcss": "^8.5.6",
         "react": "^19.2.4",
@@ -5230,6 +5231,16 @@
         }
       }
     },
+    "node_modules/next-themes": {
+      "version": "0.4.6",
+      "resolved": "https://registry.npmjs.org/next-themes/-/next-themes-0.4.6.tgz",
+      "integrity": "sha512-pZvgD5L0IEvX5/9GWyHMf3m8BKiVQwsCMHfoFosXtXBMnaS0ZnIJ9ST4b4NqLVKDEm8QBxoNNGNaBv2JNF6XNA==",
+      "license": "MIT",
+      "peerDependencies": {
+        "react": "^16.8 || ^17 || ^18 || ^19 || ^19.0.0-rc",
+        "react-dom": "^16.8 || ^17 || ^18 || ^19 || ^19.0.0-rc"
+      }
+    },
     "node_modules/next/node_modules/postcss": {
       "version": "8.4.31",
       "funding": [