feat(FN-1644): rename default global data directory from ~/.pi/fusion to ~/.fusion

- Change default global directory from ~/.pi/fusion to ~/.fusion
- Add migration logic to copy existing data from old directory to new location
- Update all core packages (store, settings, central-core, central-db) to use new default path
- Update all documentation references from ~/.pi/fusion to ~/.fusion
- Add test for ~/.pi/fusion migration path with updated mock paths
- Include changeset for @gsxdsm/fusion minor version bump

packages/dashboard/app/components/SettingsModal.tsx

@@ -18,7 +18,7 @@ import { applyPresetToSelection, generateUniquePresetId } from "../utils/modelPr
  *
  * Each section groups related settings fields under a sidebar nav item.
  * Sections have a `scope` to indicate where their settings are stored:
- *   - "global": User-level settings stored in ~/.pi/fusion/settings.json (shared across projects)
+ *   - "global": User-level settings stored in ~/.fusion/settings.json (shared across projects)
  *   - "project": Project-specific settings stored in .fusion/config.json
  *   - undefined: Section operates independently of settings storage (e.g. authentication)
  *