Remove unused packages from flake.nix

- Remove postgresql (no database used)
- Remove aider-chat (not essential)
- Remove nodePackages.npm (redundant with nodejs)

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

flake.nix

@@ -37,14 +37,9 @@
 
             # AI/Development tools
             claude-code
-            aider-chat
 
             # Node.js for Phoenix assets
             nodejs_20
-            nodePackages.npm
-
-            # Database for development
-            postgresql
 
             # Mosquito for MQTT support
             mosquitto