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/api.ts

@@ -344,7 +344,7 @@ export function fetchMemoryBackendStatus(projectId?: string): Promise<MemoryBack
   return api<MemoryBackendStatus>(withProjectId("/memory/backend", projectId));
 }
 
-/** Fetch global (user-level) settings from ~/.pi/fusion/settings.json */
+/** Fetch global (user-level) settings from ~/.fusion/settings.json */
 export function fetchGlobalSettings(): Promise<GlobalSettings> {
   return api<GlobalSettings>("/settings/global");
 }