chore: add VS Code settings.json to gitignore

- Why:
  - VS Code settings are personal IDE preferences, not shared project config
- What:
  - remove !.vscode/settings.json exception from .gitignore
- Refs: AGENTS.md

.gitignore

@@ -40,7 +40,6 @@ venv.bak/
 # =============================================================================
 # VS Code
 .vscode/*
-!.vscode/settings.json
 !.vscode/tasks.json
 !.vscode/launch.json
 !.vscode/extensions.json