Add direnv and Letta Code support

- Add .envrc for direnv configuration
- Ignore .letta directory
- Ignore .env files (with exception for .env.example)

👾 Generated with [Letta Code](https://letta.com)

Co-Authored-By: Letta <noreply@letta.com>

Author: kaaloo

.envrc

@@ -0,0 +1,2 @@
+layout node
+dotenv

.gitignore

@@ -1,2 +1,8 @@
 node_modules
-.aider*
+.aider*
+.letta
+
+# Environment variables
+.env
+.env.*
+!.env.example