feat: Implement visual experiment designer and enhance landing page

- Add drag-and-drop experiment design capabilities using @dnd-kit libraries
- Introduce new experiment-related database schema and API routes
- Enhance landing page with modern design, gradients, and improved call-to-action sections
- Update app sidebar to include experiments navigation
- Add new dependencies for experiment design and visualization (reactflow, react-zoom-pan-pinch)
- Modify study and experiment schemas to support more flexible experiment configuration
- Implement initial experiment creation and management infrastructure

drizzle/meta/_journal.json

@@ -1,5 +1,13 @@
 {
   "version": "7",
   "dialect": "postgresql",
-  "entries": []
+  "entries": [
+    {
+      "idx": 0,
+      "version": "7",
+      "when": 1739338336977,
+      "tag": "0000_adorable_grandmaster",
+      "breakpoints": true
+    }
+  ]
 }