bump zat to alpha.9 + websocket.zig to 0261b7d (client write lock)
fixes GPF in websocket client write path: concurrent writes from ping
loop, auto-pong, and close were interleaving frame headers/payloads on
the shared stream, corrupting memory during memcpy in Writer.zig.
websocket.zig 0261b7d adds _write_lock: Io.Mutex to the client, matching
the server-side Conn.lock pattern. zat alpha.9 pins the same websocket
commit, resolving the diamond dependency.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>