node: periodically re-broadcast TreeAnnounce on no-change in check_periodic_parent_reeval

Closes the eventually-consistent gap in spanning-tree state
distribution. Every existing send_tree_announce_to_all call site
gates on a local state-change event (parent switch, self-root
promotion, ancestry change, peer promotion, parent loss). Once a
partition latches — for example a parent-switch announce stranded
in the brief cross-init handshake swap window, where the announce
arrives on a session-index whose decrypt-worker entry has been
unregistered — neither side's state changes again, so neither
side ever re-broadcasts. The existing 60 s check_periodic_parent_reeval
was a re-evaluation, not a re-broadcast: it short-circuited
silently on no-change. Production-side healing depended on
incidental link churn; lab harnesses with stable docker-bridge
links had no equivalent path.

Add a final else branch that fires send_tree_announce_to_all
unconditionally on the no-change path, alongside the existing
switch and self-promote arms. Receivers coalesce by sequence
comparison (ParentDeclaration::is_fresher_than) and short-circuit
at the `if !updated` gate in handle_tree_announce; same-sequence
repeats drop silently with no cascade. The per-peer 500 ms
rate-limiter is well below this 60 s cadence and does not suppress
the heartbeat broadcast.

The fix is a general protocol-robustness improvement: it addresses
any in-flight TreeAnnounce loss class, not only the specific
cross-init swap-window drop site.

testing/static/scripts/rekey-test.sh BASELINE_CONVERGENCE_TIMEOUT
60 -> 65 so a partition healed by the periodic broadcast at T+60
lands inside the convergence window. wait_for_full_baseline
early-exits on PASS, so successful reps see no extra wall-clock.

testing/static/scripts/rekey-test.sh

@@ -145,8 +145,14 @@ fi
 # ── Full test ─────────────────────────────────────────────────────────
 trap 'echo ""; echo "Test interrupted"; exit 130' INT
 
-# Wait times derived from rekey timer
-BASELINE_CONVERGENCE_TIMEOUT=60
+# Wait times derived from rekey timer.
+# BASELINE_CONVERGENCE_TIMEOUT must cover one full daemon
+# node.tree.reeval_interval_secs (default 60) plus a small margin
+# so any partition that only heals via the periodic TreeAnnounce
+# re-broadcast lands inside the convergence window. wait_for_full_baseline
+# early-exits on PASS, so successful reps are unaffected by the
+# extra headroom.
+BASELINE_CONVERGENCE_TIMEOUT=65
 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