Termium v0.2.4 — macOS installer graphics detection

Termium v0.2.4

Fix graphics detection when the macOS installer automatically launches Termium,
or when launching with input redirected from /dev/tty.

The installer reopens terminal input because its script arrives through a pipe.
On macOS, poll() reports that reopened device as invalid, causing an immediate
fallback to ASCII graphics. Increasing the timeout in v0.2.3 did not address this
failure. Terminal queries now use select(), which supports the device; the
one-second graphics probe deadlines remain.

Debug logs now record graphics probe errors and the automatically selected
renderer. Regression tests exercise direct launch, /dev/tty redirection, and
the installer's pipe-and-launch handoff, including delayed responses and ASCII
fallback when no graphics protocol responds.

Close Termium, then update:

curl -fsSL https://termium.dev/install | bash

After quitting, termium --version should report v0.2.4.