fix: Resolve build errors with border color and import paths

- Add missing --border CSS variable for light and dark mode
- Add border color to Tailwind config using hsl(var(--border))
- Fix import paths in sidebar.tsx (@/hooks/ instead of @/components/hooks/)
- Fix import path in toaster.tsx (@/hooks/ instead of @/components/hooks/)

These fixes ensure npm run dev / npm run build work out of the box.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/app/globals.css

@@ -5,12 +5,14 @@
 :root {
   --background: #ffffff;
   --foreground: #171717;
+  --border: 220 13% 91%;
 }
 
 @media (prefers-color-scheme: dark) {
   :root {
     --background: #0a0a0a;
     --foreground: #ededed;
+    --border: 240 3.7% 15.9%;
   }
 }