feat: private accounts, explore/people merge, meal-plan fixes, i18n and theme cleanup

- Private accounts: users.isPrivate hides a user from search and their
  recipes from search/trending/for-you discovery surfaces (follow-aware
  where the route already has session context, blanket exclusion where it
  doesn't); existing followers and direct links are unaffected, no
  follow-request approval flow was built (explicit scope limit)
- Merged /people into the Explore tab (tab=people query param); the old
  standalone route now redirects there
- "Get Ideas" vs "Surprise Me" were doing the same empty-prompt call;
  Surprise Me now injects a real random constraint (5-ingredient, one-pot,
  etc.), matching the existing pattern in the AI recipe-generate dialog
- Meal-plan day cells now link to their recipe (was dead text) and gained
  a one-click "mark as cooked" action
- Theme toggle is now a real three-way light/dark/system control instead
  of a binary flip
- Nutrition goals form had zero i18n wiring; fully localized now

New migration 0027 (users.is_private) generated, left unapplied like the
others. Verified with typecheck, lint, and a clean --no-cache docker build.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/components/layout/nav.tsx

@@ -3,7 +3,7 @@
 import Link from "next/link";
 import { usePathname, useRouter } from "next/navigation";
 import { useTheme } from "next-themes";
-import { BookOpen, Calendar, Package, ChefHat, User, Rss, FolderOpen, ShoppingCart, Shield, Search, Compass, Menu, Sun, Moon, Apple } from "lucide-react";
+import { BookOpen, Calendar, Package, ChefHat, User, Rss, FolderOpen, ShoppingCart, Shield, Search, Compass, Menu, Sun, Moon, Monitor, Apple } from "lucide-react";
 import { cn } from "@/lib/utils";
 import { Button, buttonVariants } from "@/components/ui/button";
 import {
@@ -44,8 +44,13 @@ export function Nav() {
   const { data: session } = authClient.useSession();
   const isAdmin = (session?.user as { role?: string } | undefined)?.role === "admin";
   const username = (session?.user as { username?: string } | undefined)?.username;
-  const { resolvedTheme, setTheme } = useTheme();
+  const { theme, setTheme } = useTheme();
   const t = useTranslations("nav");
+  const THEME_OPTIONS = [
+    { value: "light", icon: Sun, label: t("lightMode") },
+    { value: "dark", icon: Moon, label: t("darkMode") },
+    { value: "system", icon: Monitor, label: t("systemMode") },
+  ] as const;
   return (
     <header className="sticky top-0 z-50 border-b bg-background/95 backdrop-blur supports-[backdrop-filter]:bg-background/60">
       <div className="container mx-auto flex h-14 items-center gap-6 px-4">
@@ -126,13 +131,32 @@ export function Nav() {
               <DropdownMenuItem>
                 <Link href="/settings" className="w-full">{t("settings")}</Link>
               </DropdownMenuItem>
-              <DropdownMenuItem
-                onClick={() => setTheme(resolvedTheme === "dark" ? "light" : "dark")}
-                className="flex items-center gap-2"
+              <div
+                role="group"
+                aria-label={t("systemMode")}
+                className="mx-1.5 my-1 flex items-center gap-0.5 rounded-md border bg-muted/50 p-0.5"
               >
-                {resolvedTheme === "dark" ? <Sun className="h-3.5 w-3.5" /> : <Moon className="h-3.5 w-3.5" />}
-                {resolvedTheme === "dark" ? t("lightMode") : t("darkMode")}
-              </DropdownMenuItem>
+                {THEME_OPTIONS.map(({ value, icon: Icon, label }) => (
+                  <button
+                    key={value}
+                    type="button"
+                    title={label}
+                    aria-label={label}
+                    aria-pressed={theme === value}
+                    onClick={(e) => {
+                      e.preventDefault();
+                      setTheme(value);
+                    }}
+                    className={cn(
+                      "flex flex-1 items-center justify-center rounded-sm p-1.5 text-muted-foreground transition-colors hover:text-foreground",
+                      theme === value && "bg-background text-foreground shadow-sm"
+                    )}
+                  >
+                    <Icon className="h-3.5 w-3.5" />
+                    <span className="sr-only">{label}</span>
+                  </button>
+                ))}
+              </div>
               {isAdmin && (
                 <>
                   <DropdownMenuSeparator />