Grok Telegram Bridge 0.5.1

A small bugfix release: a dead turn no longer freezes the whole lane.

What is new since 0.5.0

A cancelled turn releases the worker right away. If a turn that had
already used tools was cancelled (Esc in the terminal) or crashed, no final
answer row ever lands in the session log, and the bridge used to keep
waiting for it until the full GRB_TUI_ANSWER_TIMEOUT window (2 hours by
default) ran out - with every queued message stuck behind it. The wait loop
now double-checks the TUI screen for its busy hints (the spinner status
line and the cancel hint in the footer); when the no-progress window has
passed and two consecutive probes both see an idle screen, the turn is
treated as dead and the worker moves on with a clear reason in the error
message. When the probe is unsure (capture fails, blank pane) it keeps
waiting - a live turn is never cut on a broken instrument.
Kill switch. Set GRB_TUI_DEAD_TURN_PROBE=0 to restore the previous
behavior; GRB_TUI_DEAD_TURN_PROBE_GAP (seconds, default 3) controls the
gap between the two idle probes.
Backlog log lines now carry a timestamp, so a stuck queue can be
correlated with process restarts after the fact.