feat: dashboard, Convex auth, UI components, and LemonSpace branding

- Add dashboard shell with auth integration
- Wire Better Auth / Convex (client, server, HTTP routes)
- Add shadcn-style UI primitives and logo assets
- Update global styles and landing page
- Add internal docs (.docs)

Made-with: Cursor

convex/http.ts

@@ -0,0 +1,9 @@
+import { httpRouter } from "convex/server";
+import { authComponent, createAuth } from "./auth";
+
+const http = httpRouter();
+
+// Auth-Routen registrieren (kein CORS nötig bei Next.js — same-origin)
+authComponent.registerRoutes(http, createAuth);
+
+export default http;