feat: add app tier system — core/recommended/optional (SCALE-02, SCALE-03)

get_app_tier() classifies all apps:
- core: Bitcoin, LND, Electrs, Mempool, BTCPay, DWN, FileBrowser
- recommended: Fedimint, Grafana, Vaultwarden, Kuma, SearXNG, etc.
- optional: everything else

Tier field added to Manifest struct (data_model.rs) and exposed
via WebSocket package data for frontend tier badges.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

core/archipelago/src/api/rpc/package.rs

@@ -1030,6 +1030,7 @@ fn create_installing_entry(package_id: &str) -> PackageDataEntry {
             author: None,
             website: None,
             interfaces: None,
+            tier: None,
         },
         installed: None,
         install_progress: None,