feat(home): change claude-code default model to sonnet (#419)

## Summary

- Change `programs.claude-code.settings.model` from `"opus"` to `"sonnet"`

Stacked on #418.

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Author: stackptr

modules/home/development.nix

@@ -37,7 +37,7 @@ in {
           };
         };
         settings = {
-          model = "opus";
+          model = "sonnet";
           # Disabled in favor of Basic Memory MCP for cross-device access
           autoMemoryEnabled = false;
           permissions = {