fix(settings):Use schema defaults and only save overrides

   This change refactors the settings system to be aware of the default values defined in the settings schema.

   Key changes:
   - A new `getDefaultSettings` function generates a complete default settings object directly from the schema.
   - The settings merge process now uses these defaults as the base layer, ensuring a consistent starting point.
   - `saveSettings` is updated to compare settings against the defaults and only write the values that have been explicitly changed.

   This results in cleaner user and workspace `settings.json` files, as they will no longer be cluttered with default values. It also makes
   the settings system more robust and predictable.