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/convex.config.ts

@@ -0,0 +1,7 @@
+import { defineApp } from "convex/server";
+import betterAuth from "@convex-dev/better-auth/convex.config";
+
+const app = defineApp();
+app.use(betterAuth);
+
+export default app;