feat(seo): add metadata, sitemap, robots, JSON-LD, dynamic OG image

- Centralize brand/keyword config in lib/site.ts (slogan, 22 keywords).
- Root layout: metadataBase, title template, OG/Twitter defaults, robots rules.
- Per-page metadata: home, trips list (filter-aware), trip detail, profile (noindex).
- Layout wrappers add metadata to client-component pages: login, register, create-trip.
- Trip detail: generateMetadata + JSON-LD Event + BreadcrumbList (price, availability, rating).
- Home page: JSON-LD Organization + WebSite + SearchAction (sitelink search).
- app/sitemap.ts: dynamic sitemap pulling OPEN/FULL trips from Prisma.
- app/robots.ts: disallow /api/, /profile, /create-trip; references sitemap.
- app/trips/[id]/opengraph-image.tsx: dynamic 1200x630 OG image per trip with
  cover photo, title, mountain, date, price, brand badge.
- Seeder: switch trip images from local SVG placeholders to real Unsplash CDN URLs.
- Drop 18 obsolete seed SVGs from public/images/seed/.

New env: NEXT_PUBLIC_SITE_URL (defaults to localhost:3000) — set to prod domain on deploy.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/create-trip/layout.tsx

@@ -0,0 +1,13 @@
+import type { Metadata } from "next";
+
+export const metadata: Metadata = {
+  title: "Buat Open Trip",
+  description:
+    "Buat open trip pendakian gunung di SeTrip. Atur itinerary, harga, dan ajak pendaki lain ikut serta.",
+  alternates: { canonical: "/create-trip" },
+  robots: { index: false, follow: false },
+};
+
+export default function CreateTripLayout({ children }: { children: React.ReactNode }) {
+  return children;
+}