feat: add navigation_failed signal with time-based stuck detection and simulation pipeline

NpcVisual:
- Add navigation_failed(sim_id) signal distinct from arrived_at_target
  so the simulation layer can distinguish genuine arrival from failure
- Replace integer stuck_counter with delta-based stuck_time and
  exported stuck_timeout (1.5s) for frame-rate-independent detection
- Add path_request_id / path_pending mechanism to reject stale
  async path results when a new target is set or NPC dies
- On empty path or stuck movement, emit navigation_failed instead
  of arriving; only emit arrived_at_target when truly close to target
- Reduce arrival_distance back to 0.6 now that navigation_failure
  is properly signalled (no longer needed as a workaround)
- clamp arrival_distance reference in apply_dead_visual_state

SimNPC:
- Remove retry_count (replaced by navigation_failed signal pathway)
- Move last_task assignment from set_task() to task completion in
  SimulationManager so it reflects the task that actually finished

SimulationManager:
- Add notify_npc_navigation_failed(): release reservation, record
  last_task, send NPC to wander for 2s, emit task_changed signal
- Add notify_npc_target_unavailable() as public alias of above
- Guard extraction with node.reserved_by == npc.id to prevent
  stale/illegitimate extraction when reservation is lost
- Guard fallback zone task completion (apply_npc_task) so it only
  fires for non-resource tasks (gather_food/wood with no target
  silently skip instead of applying zone values)
- Remove retry_count safety net (fully replaced by signal pipeline)

WorldViewManager:
- Connect navigation_failed signal in spawn_npc_visual()
- Skip target assignment for empty/idle/dead task states
- When no resource node available for gather_food/wood, call
  notify_npc_target_unavailable() so NPC wanders instead of idling
- Add _on_npc_visual_navigation_failed handler delegating to
  SimulationManager.notify_npc_navigation_failed()
- Remove retry_count references

simulation/SimNPC.gd

@@ -28,7 +28,6 @@ var task_duration := 0.0
 var task_progress := 0.0
 var task_complete := true
 var target_id: StringName = &""
-var retry_count := 0
 var last_task := ""
 
 func _init(
@@ -247,7 +246,6 @@ func calculate_task_score(
 	return score
 
 func set_task(task: String, duration: float) -> void:
-	last_task = current_task
 	current_task = task
 	task_duration = duration
 	task_progress = 0.0

simulation/SimulationManager.gd

@@ -87,21 +87,25 @@ func simulate_tick() -> void:
 
 			if npc.target_id != &"":
 				var node := ResourceNode.get_by_id(npc.target_id)
-				if node != null:
+				if node != null and node.reserved_by == npc.id:
 					var extracted := node.extract()
 					if extracted > 0:
 						village.apply_resource_delta(node.resource_id, extracted)
 						if DEBUG_LOGS:
 							print("[SimulationManager] ", npc.npc_name, " extracted ", extracted, " ", node.resource_id, " from ", node.node_id)
+				elif DEBUG_LOGS:
+					print("[SimulationManager] ", npc.npc_name, " could not complete ", completed_task, ": target reservation was invalid")
 				release_npc_reservation(npc.id)
-			else:
+			elif completed_task not in ["gather_food", "gather_wood"]:
 				village.apply_npc_task(npc)
+			elif DEBUG_LOGS:
+				print("[SimulationManager] ", npc.npc_name, " could not complete ", completed_task, ": no resource target")
 
 			village_was_changed = true
-			npc.retry_count = 0
 
 			npc.task_complete = true
 			npc.task_state = SimNPC.TASK_STATE_IDLE
+			npc.last_task = completed_task
 			npc.current_task = "idle"
 
 			if needs_immediate_food_after_gather and village.food > 0:
@@ -111,15 +115,6 @@ func simulate_tick() -> void:
 				if DEBUG_LOGS:
 					print("[SimulationManager] ", npc.npc_name, " gathered food while starving and is going to eat immediately.")
 
-		if npc.task_state == SimNPC.TASK_STATE_TRAVELING and npc.target_id == &"":
-			npc.retry_count += 1
-			if npc.retry_count >= 5:
-				if DEBUG_LOGS:
-					print("[SimulationManager] ", npc.npc_name, " stuck traveling without target for ", npc.retry_count, " attempts, replanning")
-				npc.task_state = SimNPC.TASK_STATE_IDLE
-				npc.current_task = ""
-				npc.retry_count = 0
-
 		if DEBUG_LOGS:
 			print(
 				npc.npc_name,
@@ -184,10 +179,7 @@ func notify_npc_arrived(npc_id: int) -> void:
 					if node == null or not node.can_extract():
 						if DEBUG_LOGS:
 							print("[SimulationManager] ", npc.npc_name, " arrived but target ", npc.target_id, " is unavailable, replanning")
-						release_npc_reservation(npc.id)
-						npc.task_state = SimNPC.TASK_STATE_IDLE
-						npc.current_task = ""
-						npc.retry_count += 1
+						notify_npc_navigation_failed(npc.id)
 						return
 
 				npc.start_working()
@@ -196,6 +188,26 @@ func notify_npc_arrived(npc_id: int) -> void:
 					print("[SimulationManager] ", npc.npc_name, " arrived and started working on: ", npc.current_task)
 			return
 
+func notify_npc_navigation_failed(npc_id: int) -> void:
+	for npc in npcs:
+		if npc.id != npc_id:
+			continue
+		if npc.is_dead or npc.task_state != SimNPC.TASK_STATE_TRAVELING:
+			return
+
+		var failed_task := npc.current_task
+		release_npc_reservation(npc.id)
+		npc.last_task = failed_task
+		npc.set_task("wander", 2.0)
+		npc_task_changed.emit(npc, failed_task, npc.current_task)
+
+		if DEBUG_LOGS:
+			print("[SimulationManager] ", npc.npc_name, " could not navigate for ", failed_task, " and is trying a wander target")
+		return
+
+func notify_npc_target_unavailable(npc_id: int) -> void:
+	notify_npc_navigation_failed(npc_id)
+
 func eat_food(amount: float) -> void:
 	village.food -= amount
 	village_changed.emit(village)