fix(radio): restore upstream token-bucket duty-cycle enforcement

Commit 22eb9b87 ("Revert 'Merge remote-tracking branch origin/dev...'")
reverted an entire upstream merge to escape a bad merge state, dropping
860 lines across 66 files. Among the collateral never reconciled on a
later re-merge was eb4fa032's token-bucket duty-cycle enforcement — the
mechanism that keeps nodes under a configured airtime budget (and EU
868 MHz nodes under the legally-mandated duty cycle). The fork had fallen
back to fixed per-packet spacing (getAirtimeBudgetFactor reverted to 2.0),
losing the windowed enforcement.

This was never an intentional design choice, so restoring it re-aligns the
fork with upstream and REDUCES the merge-conflict surface: Dispatcher.{h,cpp}
now diverge from upstream by watchdog additions only (77 insertions, 0
deletions) instead of rewriting checkSend()/loop().

Restored from upstream: updateTxBudget/tx_budget_ms/duty_cycle_window_ms/
getRemainingTxBudget/getDutyCycleWindowMs and the windowed budget logic in
Dispatcher; getOutboundTotal() and the 0xFFFFFFFF count-all sentinel in
StaticPoolPacketManager; the getOutboundTotal() call in StatsFormatHelper.
Re-applied the fork's MQTT radio-watchdog on top as pure additions
(#ifdef WITH_MQTT_BRIDGE), keeping formatRadioDiag.

Stored airtime_factor settings keep their meaning: fork's t*factor spacing
and upstream's 1/(1+factor) windowed budget yield the same steady-state
duty cycle; upstream additionally allows short bursts within the window.

Phase 2 (CAD / radio_fem_rxgain, which touch NodePrefs persistence and
per-board FEM wiring) is documented in RESTORE_UPSTREAM_NOTES.md, not done
here. Builds: Heltec_v3 observer + plain repeater. NEEDS ON-DEVICE
duty-cycle validation before merge.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/helpers/StaticPoolPacketManager.cpp

@@ -9,6 +9,8 @@ PacketQueue::PacketQueue(int max_entries) {
 }
 
 int PacketQueue::countBefore(uint32_t now) const {
+  if (now == 0xFFFFFFFF) return _num;  // sentinel: count all entries regardless of schedule
+
   int n = 0;
   for (int j = 0; j < _num; j++) {
     if ((int32_t)(_schedule_table[j] - now) > 0) continue;   // scheduled for future... ignore for now
@@ -97,6 +99,10 @@ int  StaticPoolPacketManager::getOutboundCount(uint32_t now) const {
   return send_queue.countBefore(now);
 }
 
+int  StaticPoolPacketManager::getOutboundTotal() const {
+  return send_queue.count();
+}
+
 int StaticPoolPacketManager::getFreeCount() const {
   return unused.count();
 }