test(rekey): bump Phase 1 baseline-convergence headroom 36s → 60s

The Phase 1 pre-rekey baseline in `wait_for_full_baseline`
occasionally times out on GitHub-hosted runners with one ping pair
failing to converge inside the BASELINE_CONVERGENCE_TIMEOUT window.
Phases 2–6 always pass cleanly when this happens — the rekey itself
is fine, the mesh just hasn't finished spanning-tree + bloom-filter
convergence by the time Phase 1 starts pinging.

The wait loop returns as soon as all 20 pairs converge, so the cost
on the success path is unchanged (typical local CI returns well
under the old 36s). The bump only adds headroom on the failure
path. Operators previously worked around this with
`gh run rerun --failed`; this aims to retire that workaround for
the IK/XK lines.

Distinct from the next-branch XX rekey dual-init race, which is a
real protocol bug tracked separately.

testing/static/scripts/rekey-test.sh

@@ -146,7 +146,7 @@ fi
 trap 'echo ""; echo "Test interrupted"; exit 130' INT
 
 # Wait times derived from rekey timer
-BASELINE_CONVERGENCE_TIMEOUT=36
+BASELINE_CONVERGENCE_TIMEOUT=60
 REKEY_SETTLE=12        # > DRAIN_WINDOW_SECS (10) so post-rekey samples are off the old session
 # First FMP rekey should follow shortly after the 35s interval once the mesh is
 # fully converged. Keep this bounded to preserve a meaningful scheduling check