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

player/npc/NpcVisual.gd

@@ -1,12 +1,14 @@
 extends CharacterBody3D
 
 signal arrived_at_target(sim_id: int)
+signal navigation_failed(sim_id: int)
 
 const DEBUG_LOGS := true
 
 @export var move_speed := 3.0
 @export var rotation_speed := 8.0
 @export var waypoint_reached_distance := 0.35
+@export var stuck_timeout := 1.5
 
 @onready var nav_agent: NavigationAgent3D = $NavigationAgent3D
 
@@ -18,8 +20,10 @@ var profession: String = ""
 var current_path: PackedVector3Array = []
 var path_index := 0
 var current_target := Vector3.INF
-var arrival_distance := 1.5
-var stuck_counter := 0
+var arrival_distance := 0.6
+var stuck_time := 0.0
+var path_request_id := 0
+var path_pending := false
 
 var is_dead_visual := false
 var dead_material := StandardMaterial3D.new()
@@ -38,8 +42,12 @@ func setup_from_sim(npc: SimNPC) -> void:
 	name = "NPC_%s_%s" % [sim_id, npc_name]
 
 func set_target_position(pos: Vector3) -> void:
+	path_request_id += 1
+	var request_id := path_request_id
 	current_target = pos
 	has_reported_arrival = false
+	stuck_time = 0.0
+	path_pending = false
 
 	if global_position.distance_to(pos) <= arrival_distance:
 		current_path = PackedVector3Array()
@@ -48,9 +56,13 @@ func set_target_position(pos: Vector3) -> void:
 		return
 
 	nav_agent.target_position = pos
+	path_pending = true
 
 	await get_tree().physics_frame
 
+	if request_id != path_request_id or is_dead_visual:
+		return
+
 	current_path = NavigationServer3D.map_get_path(
 		get_world_3d().navigation_map,
 		global_position,
@@ -58,11 +70,12 @@ func set_target_position(pos: Vector3) -> void:
 		true
 	)
 
+	path_pending = false
 	path_index = 0
 
 	if current_path.is_empty():
-		debug_log("Path is empty, stuck counter will handle fallback.")
-		nav_agent.target_position = global_position
+		debug_log("Path is empty")
+		_report_navigation_failure_once()
 	else:
 		debug_log("New target: %s Path points: %s" % [pos, current_path.size()])
 
@@ -77,6 +90,11 @@ func _physics_process(delta: float) -> void:
 		move_and_slide()
 		return
 
+	if path_pending:
+		velocity = Vector3.ZERO
+		move_and_slide()
+		return
+
 	if global_position.distance_to(current_target) <= arrival_distance:
 		_report_arrival_once()
 		velocity = Vector3.ZERO
@@ -86,10 +104,7 @@ func _physics_process(delta: float) -> void:
 	if current_path.is_empty() or path_index >= current_path.size():
 		velocity = Vector3.ZERO
 		move_and_slide()
-		stuck_counter += 1
-		if stuck_counter > 90:
-			debug_log("Stuck with no valid path, reporting arrival")
-			_report_arrival_once()
+		_report_navigation_failure_once()
 		return
 
 	var next_pos := current_path[path_index]
@@ -109,14 +124,15 @@ func _physics_process(delta: float) -> void:
 
 	move_and_slide()
 
-	if global_position.distance_squared_to(prev_pos) < 0.001:
-		stuck_counter += 1
-		if stuck_counter > 90:
-			debug_log("Stuck while navigating, reporting arrival")
-			_report_arrival_once()
+	var minimum_progress := move_speed * delta * 0.1
+	if global_position.distance_squared_to(prev_pos) < minimum_progress * minimum_progress:
+		stuck_time += delta
+		if stuck_time >= stuck_timeout:
+			debug_log("Movement remained blocked")
+			_report_navigation_failure_once()
 			return
 	else:
-		stuck_counter = 0
+		stuck_time = 0.0
 
 	var target_angle := atan2(direction.x, direction.z)
 	rotation.y = lerp_angle(rotation.y, target_angle, rotation_speed * delta)
@@ -132,12 +148,28 @@ func _report_arrival_once() -> void:
 	debug_log("Arrived at target")
 	arrived_at_target.emit(sim_id)
 
+func _report_navigation_failure_once() -> void:
+	if has_reported_arrival:
+		return
+
+	has_reported_arrival = true
+	current_path = PackedVector3Array()
+	path_index = 0
+	current_target = Vector3.INF
+	path_pending = false
+	velocity = Vector3.ZERO
+
+	debug_log("Navigation failed")
+	navigation_failed.emit(sim_id)
+
 func apply_dead_visual_state() -> void:
 	is_dead_visual = true
+	path_request_id += 1
 	velocity = Vector3.ZERO
 	current_path = PackedVector3Array()
 	path_index = 0
 	current_target = Vector3.INF
+	path_pending = false
 	has_reported_arrival = true
 
 	scale = Vector3(0.8, 0.25, 1.2)