The effects guide gives the JS park its deadline, as it gives the C one, and names select, not poll, in io_sys()

[aldeni]

What changes

Two edits in one paragraph of guide/EFFECTS.md, "The JS side":

 `more()` when `fd` is ready; `more` answers the value, or `undefined` to
-park again. `io_sys()` is `libc` through `bun:ffi`
-(`read`, `recv`, `poll`, `errno`); `tcp_recv.js` shows the full shape.
+park again. Add an absolute `performance.now()` deadline as a fifth
+argument to also wake on time. `io_sys()` is `libc` through `bun:ffi`
+(`read`, `recv`, `select`, `errno`); `tcp_recv.js` shows the full shape.

Why

• The C side says how a park also wakes on time ("Replace 0 with an
  absolute io_tick() deadline", since Fix stale C helper calls in the effects guide #947). The JS side showed only
  io_park_on(fd, out, k, more). The JS runtime's io_park_on has taken
  a fifth argument, at, since TCP.poll (TCP.poll is a receive with a deadline: a park waits on its fd and its clock, whichever fires first (#858) #861), and tcp_poll.js uses
  it. It is an absolute performance.now() time in ms: io_wait turns it
  into select's timeout and compares it with performance.now(). If you
  leave it out, the park waits on fd alone. The argument appears only in
  the runtime source inside comp.ts, and no Base signature shows it. So
  someone writing a JS twin of a timed C effect cannot find it.
• io_sys() has had no poll since the JS loop moved to select in
  A read parked on a FIFO sees its end on macOS: the IO loop waits with select (#928) #932. io_sys().poll is undefined, and select is the call it binds.

How it was checked

Linux x86-64, Bun 1.3.11, clang 22.1.8. I did not run it on macOS.

• A throwaway effect opens a pipe that nobody writes. It parks on the read
  end with io_park_on(p[0], false, k, more, performance.now() + 50), and
  more reports how long the park lasted. Its C twin parks with
  io_wait_on(w, fd, POLLIN, io_tick() + 50 ms, more). Over four runs:

  lane	empty pipe, 50 ms	one byte, 1 s	no fd, 50 ms
  bend main.bend	50.6-51.4 ms	0.0-0.1 ms	50.2-50.5 ms
  -o x.js && bun x.js	50.7-50.8 ms	0.0 ms	50.2-50.3 ms
  -o x && ./x	50.1 ms	0.0 ms	50.1 ms

  On every lane, the empty-pipe wake comes after the deadline and its read
  finds nothing.

• Without the fifth argument, the same park on the empty pipe does not
  wake within 3 s.

• typeof io_sys().poll is "undefined" and typeof io_sys().select is
  "function", on both JS lanes.

• bun gates/repo.ts: 46 / 46. The guide is 1592 ttok, under its cap of
  1600.

No test is added because the change is to the guide only.
tests/io/tcp_poll.bend already exercises the JS deadline through
TCP.poll.