fix(web client): register the thread.permissions_changed runtime event

#6470 added the thread.permissions_changed runtime event, but the embedded web
client's STREAM_EVENT_NAMES did not list it, so the Version drift job's runtime
web client test (registers the full emitted Runtime vocabulary) failed on the
hosted run for 34bf6568f2 (35 listed vs 36 emitted).

Evidence (2026-10-10): node --test crates/tui/tests/runtime_web_client.test.mjs
43 passed, 0 failed (was 42 passed, 1 failed in hosted run 38044517173).
Not verified: hosted CI on this commit.

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

crates/tui/src/runtime_web/app.mjs

@@ -2,6 +2,7 @@ export const STREAM_EVENT_NAMES = [
   "thread.started",
   "thread.updated",
   "thread.forked",
+  "thread.permissions_changed",
   "turn.started",
   "turn.lifecycle",
   "turn.usage",