fix: Use React Router Link for nav to prevent scroll reset

Changed sidebar NavLink from <a> to <Link> for client-side navigation.
This prevents full page reload and scroll position reset.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

cannaiq/src/components/Layout.tsx

@@ -1,5 +1,5 @@
 import { ReactNode, useEffect, useState } from 'react';
-import { useNavigate, useLocation } from 'react-router-dom';
+import { useNavigate, useLocation, Link } from 'react-router-dom';
 import { useAuthStore } from '../store/authStore';
 import { api } from '../lib/api';
 import { StateSelector } from './StateSelector';
@@ -48,8 +48,8 @@ interface NavLinkProps {
 
 function NavLink({ to, icon, label, isActive }: NavLinkProps) {
   return (
-    <a
-      href={to}
+    <Link
+      to={to}
       className={`flex items-center gap-3 px-3 py-2 rounded-lg text-sm font-medium transition-colors ${
         isActive
           ? 'bg-emerald-50 text-emerald-700'
@@ -58,7 +58,7 @@ function NavLink({ to, icon, label, isActive }: NavLinkProps) {
     >
       <span className={`flex-shrink-0 ${isActive ? 'text-emerald-600' : 'text-gray-400'}`}>{icon}</span>
       <span>{label}</span>
-    </a>
+    </Link>
   );
 }