fix(frontend): move search to header center on mobile, nav links in hamburger only

thoughts-frontend/components/main-nav.tsx

@@ -32,32 +32,11 @@ export function MainNav({ isLoggedIn }: MainNavProps) {
 
   return (
     <>
-      {/* Desktop nav */}
-      <nav className="hidden md:flex items-center space-x-6 text-sm font-medium">
-        {links.map(({ href, label }) => (
-          <Link
-            key={href}
-            href={href}
-            className={cn(
-              "transition-colors hover:text-foreground/80",
-              pathname === href ? "text-foreground" : "text-foreground/60"
-            )}
-          >
-            {label}
-          </Link>
-        ))}
-        <SearchInput />
-      </nav>
-
-      {/* Mobile hamburger */}
+      {/* Mobile: hamburger + search fills center */}
+      <div className="flex md:hidden items-center gap-2 flex-1 mx-2">
         <Sheet open={open} onOpenChange={setOpen}>
           <SheetTrigger asChild>
-          <Button
-            variant="ghost"
-            size="icon"
-            className="md:hidden"
-            aria-label="Open menu"
-          >
+            <Button variant="ghost" size="icon" aria-label="Open menu" className="shrink-0">
               <Menu className="h-5 w-5" />
             </Button>
           </SheetTrigger>
@@ -82,11 +61,29 @@ export function MainNav({ isLoggedIn }: MainNavProps) {
                 </Link>
               ))}
             </nav>
-          <div className="mt-6">
-            <SearchInput />
-          </div>
           </SheetContent>
         </Sheet>
+        <div className="flex-1">
+          <SearchInput />
+        </div>
+      </div>
+
+      {/* Desktop nav */}
+      <nav className="hidden md:flex items-center space-x-6 text-sm font-medium">
+        {links.map(({ href, label }) => (
+          <Link
+            key={href}
+            href={href}
+            className={cn(
+              "transition-colors hover:text-foreground/80",
+              pathname === href ? "text-foreground" : "text-foreground/60"
+            )}
+          >
+            {label}
+          </Link>
+        ))}
+        <SearchInput />
+      </nav>
     </>
   );
 }

thoughts-frontend/components/search-input.tsx

@@ -17,7 +17,7 @@ export function SearchInput() {
   };
 
   return (
-    <form onSubmit={handleSearch} className="relative w-full max-w-sm">
+    <form onSubmit={handleSearch} className="relative w-full md:max-w-sm">
       <SearchIcon className="absolute left-3 top-1/2 -translate-y-1/2 h-4 w-4 text-muted-foreground" />
       <Input
         name="q"