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

lib/auth-client.ts

@@ -0,0 +1,7 @@
+import { createAuthClient } from "better-auth/react";
+import { convexClient } from "@convex-dev/better-auth/client/plugins";
+
+// Next.js: kein crossDomainClient nötig (same-origin via API Route Proxy)
+export const authClient = createAuthClient({
+  plugins: [convexClient()],
+});

lib/auth-server.ts

@@ -0,0 +1,19 @@
+import { convexBetterAuthNextJs } from "@convex-dev/better-auth/nextjs";
+
+export const {
+  handler,              // Route Handler für /api/auth/*
+  preloadAuthQuery,     // SSR: Query mit Auth vorladen
+  isAuthenticated,      // Check ob User eingeloggt ist
+  getToken,             // JWT Token abrufen
+  fetchAuthQuery,       // Server-side: Convex Query mit Auth
+  fetchAuthMutation,    // Server-side: Convex Mutation mit Auth
+  fetchAuthAction,      // Server-side: Convex Action mit Auth
+} = convexBetterAuthNextJs({
+  convexUrl: process.env.NEXT_PUBLIC_CONVEX_URL!,
+  convexSiteUrl: process.env.NEXT_PUBLIC_CONVEX_SITE_URL!,
+  // JWT-Caching für schnellere SSR (optional, aber empfohlen)
+  jwtCache: {
+    enabled: true,
+    isAuthError: (error) => /auth/i.test(String(error)),
+  },
+});

lib/auth.ts

@@ -0,0 +1,6 @@
+import { betterAuth } from "better-auth";
+
+export const auth = betterAuth({
+  secret: process.env.BETTER_AUTH_SECRET,
+  url: process.env.BETTER_AUTH_URL
+});