feat: ship the ssh terminal as a first-party in-process plugin

Adds a hardcoded process:transport-owner tier so the terminal can own its
WebSocket server and ssh2 clients, which cannot cross the worker boundary.

src/types/ui-types.ts

@@ -372,6 +372,7 @@ export type AdminSection =
   | "api-keys"
   | "audit-log"
   | "ssl"
+  | "plugins"
   | "touch-input";
 export type ThemeId =
   | "dark"