feat(tema): açık / koyu / sistem teması

- TemaSaglayici (next-themes) + alt bilgide TemaSecici
- globals.css: .dark bloğunda palet token'ları çevrilir; bileşenlere
  dark: sınıfı yazılmaz
- yüzeyler bg-white → bg-card, koyu haplar text-slate-50, SVG'lerde
  sabit renk yerine değişken
- DESIGN.md §2.3 + tasarim-denetim kuralları (yuzey-beyaz,
  koyu-hap-beyaz-yazi, dark-sinif), AGENTS.md karanlık mod bölümü
- docs: koyu tema denetimi raporu

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/app/page.tsx

@@ -243,7 +243,7 @@ export default function Home() {
           </div>
           <div
             aria-hidden
-            className="pointer-events-none absolute inset-0 -z-10 bg-[radial-gradient(ellipse_58%_52%_at_50%_42%,rgba(248,250,252,0.9)_25%,rgba(248,250,252,0)_75%)]"
+            className="pointer-events-none absolute inset-0 -z-10 bg-[radial-gradient(ellipse_58%_52%_at_50%_42%,color-mix(in_oklab,var(--color-slate-50)_90%,transparent)_25%,transparent_75%)]"
           />
           <Parallax
             fromStart
@@ -257,7 +257,7 @@ export default function Home() {
             >
               <HeroForm />
             </div>
-            <div className="mt-3 inline-flex items-center gap-2.5 rounded-lg border border-slate-200 bg-white px-3 py-2 text-left text-xs text-slate-700 shadow-xs">
+            <div className="mt-3 inline-flex items-center gap-2.5 rounded-lg border border-slate-200 bg-card px-3 py-2 text-left text-xs text-slate-700 shadow-xs">
               <span>
                 <strong className="font-semibold text-slate-900">
                   Veri: YÖK Atlas
@@ -364,7 +364,7 @@ export default function Home() {
             <Parallax strength={7} className="mt-12 grid gap-6 md:grid-cols-3">
               {steps.map((s, i) => (
                 <Reveal key={s.step} delay={i * 0.08} className="h-full">
-                  <div className="relative h-full rounded-2xl border border-slate-200/70 bg-white p-8 shadow-sm transition-all duration-300 hover:-translate-y-1 hover:border-orange-500 hover:shadow-lg hover:shadow-orange-500/5">
+                  <div className="relative h-full rounded-2xl border border-slate-200/70 bg-card p-8 shadow-sm transition-all duration-300 hover:-translate-y-1 hover:border-orange-500 hover:shadow-lg hover:shadow-orange-500/5">
                     <span className="absolute -top-4 left-8 flex size-8 items-center justify-center rounded-full bg-orange-500 font-heading text-sm font-bold text-white">
                       {s.step}
                     </span>
@@ -385,7 +385,7 @@ export default function Home() {
             <Parallax strength={10} className="mx-auto mt-12 w-full max-w-3xl">
               <Reveal
                 delay={0.1}
-                className="overflow-hidden rounded-2xl border border-slate-200/70 bg-white shadow-sm"
+                className="overflow-hidden rounded-2xl border border-slate-200/70 bg-card shadow-sm"
               >
                 <dl className="grid grid-cols-1 divide-y divide-slate-200 sm:grid-cols-3 sm:divide-x sm:divide-y-0">
                   {[
@@ -466,10 +466,10 @@ export default function Home() {
                 lg'de klasik dört sütunlu tablo. */}
             <Parallax strength={7} className="mt-12">
               <Reveal delay={0.08}>
-                <div className="rounded-2xl border border-slate-200/70 bg-white shadow-sm lg:hidden">
+                <div className="rounded-2xl border border-slate-200/70 bg-card shadow-sm lg:hidden">
                   <div
                     aria-hidden
-                    className="sticky top-24 z-10 grid grid-cols-3 sm:top-32 gap-2 rounded-t-2xl border-b border-slate-100 bg-white/95 px-3 py-3 text-center text-sm font-semibold text-slate-500 backdrop-blur"
+                    className="sticky top-24 z-10 grid grid-cols-3 sm:top-32 gap-2 rounded-t-2xl border-b border-slate-100 bg-card/95 px-3 py-3 text-center text-sm font-semibold text-slate-500 backdrop-blur"
                   >
                     <span>Robotlar ve botlar</span>
                     <span>İnsan danışman</span>
@@ -508,7 +508,7 @@ export default function Home() {
                   </ul>
                 </div>
 
-                <div className="hidden overflow-hidden rounded-2xl border border-slate-200/70 bg-white shadow-sm lg:block">
+                <div className="hidden overflow-hidden rounded-2xl border border-slate-200/70 bg-card shadow-sm lg:block">
                   <Table>
                     <TableHeader>
                       <TableRow className="bg-slate-50 hover:bg-slate-50">
@@ -590,7 +590,7 @@ export default function Home() {
             >
               <Reveal
                 delay={0.08}
-                className="rounded-2xl border-2 border-orange-500 bg-white p-8 shadow-sm"
+                className="rounded-2xl border-2 border-orange-500 bg-card p-8 shadow-sm"
               >
                 <div className="flex flex-wrap items-baseline justify-between gap-2">
                   <h3 className="font-heading text-xl font-bold">
@@ -643,7 +643,7 @@ export default function Home() {
 
               <Reveal
                 delay={0.16}
-                className="flex h-fit flex-col rounded-2xl border border-slate-200/70 bg-white p-6 shadow-sm sm:w-56"
+                className="flex h-fit flex-col rounded-2xl border border-slate-200/70 bg-card p-6 shadow-sm sm:w-56"
               >
                 <div className="flex items-center gap-2">
                   <Coins className="size-4 text-amber-500" aria-hidden />
@@ -691,7 +691,7 @@ export default function Home() {
                 <Accordion
                   type="single"
                   collapsible
-                  className="mt-10 rounded-2xl border border-slate-200/70 bg-white px-6 shadow-sm"
+                  className="mt-10 rounded-2xl border border-slate-200/70 bg-card px-6 shadow-sm"
                 >
                   {faqs.map((faq) => (
                     <AccordionItem