pxx 2.3.6

The "init-watchdog" follow-up, re-scoped by the evidence: the pre-loop network
ops (memory-embed 30s, MCP-handshake 30s, model-fingerprint 2s) are already
individually bounded — but pxx's git subprocess helpers were not, so a
wedged git or a blocking git hook (a pre-commit prompt, a credential helper)
could hang a run, most dangerously at the safety-net tie which runs at startup,
before the run's own wall-clock budget exists.

Fixed

• Every git subprocess in the run path is now time-bounded and killed +
  reaped on timeout (gitenv.communicate_bounded), matching what the test-runner
  and worktree helpers already did. The three previously-unbounded helpers —
  safety_net._git (startup safety net, pre-budget), loop._git (per-round
  changed-paths/diff), and goal._git (task-DAG git) — degrade on timeout
  (git-unavailable / non-zero) instead of hanging. Bound is PXX_GIT_TIMEOUT
  seconds (default 60; positive-finite, else the default).