feat(vscode): proposal for WendyOS#1238

[Joannis]

The CLI gained a wendy fleet namespace with three commands: wendy fleet group ls|show|add|rm (device group management), wendy fleet apps [--group <g>] (per-group app inventory), and wendy fleet run --group <g> (fan-out deploy). The extension should surface these by:

1. Adding a FleetManager model that wraps the new CLI commands (fleet group ls, fleet group show, fleet group add, fleet group rm, fleet apps, fleet run).
2. Adding a FleetProvider tree-view sidebar provider that lists groups (from fleet group ls --json) and their member devices (from fleet group show --json), with commands to add/remove devices from groups and run fleet apps or fleet run against a group.
3. Registering the new wendyFleet.* commands in extension.ts.
4. Adding the new view, commands, and menus to package.json.