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.

scripts/plugin-manifest.schema.json

@@ -119,6 +119,7 @@
           "notify.send",
           "users.read",
           "process.sidecar",
+          "process:transport-owner",
           "ui.tab",
           "ui.rail",
           "ui.card",