feat: move the terminal fully into the ssh-terminal plugin (B9)

scripts/check-shell-plugin-ids.cjs

@@ -8,8 +8,7 @@
  * needs from a plugin comes through the registries instead.
  *
  * A few literals are data rather than knowledge of a plugin: host protocol
- * names that are columns on the host until Phase B moves them, and the
- * terminal's own websocket, which lives in core until the terminal moves.
+ * names that are columns on the host until Phase B moves them.
  * Those are listed with a reason in scripts/shell-plugin-id-allowlist.json,
  * which fails too when an entry stops being needed, so it only shrinks.
  */