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/cli/skill/fusion/references/task-structure.md

@@ -138,7 +138,7 @@ What the task should accomplish.
 
 ## Global Settings
 
-User-level settings at `~/.pi/fusion/settings.json`:
+User-level settings at `~/.fusion/settings.json`:
 
 ```json
 {
@@ -152,7 +152,7 @@ User-level settings at `~/.pi/fusion/settings.json`:
 
 ## Central Database (Multi-Project)
 
-For multi-project setups: `~/.pi/fusion/fusion-central.db`
+For multi-project setups: `~/.fusion/fusion-central.db`
 - Project registry
 - Unified activity feed
 - Global concurrency management