fix(dashboard): reap PTY bridge on child EOF, not only in writer finally (#54190)

The /api/pty handler only closed the PtyBridge in the writer loop's finally.
On child EOF the reader task closes the WebSocket, but if the handler task is
cancelled the instant the socket closes, the writer's finally can be skipped
and the PTY fds leak (#54028) — the FD-leak the regression test guards. Under
dashboard auto-reconnect this stacks orphaned PTYs until fds are exhausted.

Reap the bridge in the reader's EOF finally too (close() is idempotent), so
the PTY is reaped independently of the writer-loop cancellation race. Harden
the regression test to poll for teardown instead of asserting on the same
tick. Was flaky on main (2/20); now 25/25.

hermes_cli/web_server.py

@@ -12210,6 +12210,16 @@ async def pty_ws(ws: WebSocket) -> None:
             # handler never reaches its ``finally`` and the PTY's fds leak.
             # With dashboard auto-reconnect (#52962) every dropped socket then
             # stacks a fresh PTY on top of the orphaned one, exhausting fds.
+            #
+            # Reap the bridge here too (close() is idempotent): on child EOF the
+            # writer loop's ``finally`` is the usual closer, but if the handler
+            # task is cancelled the instant we close the WS, that ``finally``
+            # can be skipped, leaking the PTY. Closing from the EOF path makes
+            # the reap independent of that cancellation race (#54028).
+            try:
+                await asyncio.to_thread(bridge.close)
+            except Exception:
+                pass
             try:
                 await ws.close()
             except Exception: