feat(altyapı): yerel MongoDB, Axum backend ve Vite frontend iskeleti

- docker-compose.dev.yml: MongoDB 7, tek düğümlü replica set (port 27020)
- Backend: Axum + tokio, GET /api/health
- Frontend: React + TypeScript + Vite, /api proxy, geçici durum ekranı
- Kök package.json: npm run dev ile DB + backend + frontend
- backend/api.http örnek istekler

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/index.css

@@ -0,0 +1,37 @@
+/* Faz 0 geçici stil. Faz 2'de TailwindCSS ile değiştirilecek. */
+:root {
+  font-family: Inter, system-ui, sans-serif;
+  color-scheme: light dark;
+  background: #fafaf9;
+  color: #1c1917;
+}
+
+@media (prefers-color-scheme: dark) {
+  :root {
+    background: #1c1917;
+    color: #f5f5f4;
+  }
+}
+
+body {
+  margin: 0;
+}
+
+.placeholder {
+  min-height: 100dvh;
+  display: grid;
+  place-content: center;
+  text-align: center;
+  gap: 0.25rem;
+  padding: 1rem;
+}
+
+.placeholder h1 {
+  margin: 0;
+  font-size: 2.5rem;
+}
+
+.status {
+  margin-top: 1.5rem;
+  font-variant-numeric: tabular-nums;
+}