feat: add deterministic simulation foundation

Replace implicit randomness with seeded per-NPC RandomNumberGenerator
streams so the same seed always produces the same scenario outcome.

- Add SimulationClock (RefCounted): explicit fixed-step clock that
  converts frame delta into simulation ticks while preserving sub-tick
  remainder; replaces raw _process tick_timer accumulation
- Add simulation_seed export (int=1337) to SimulationManager; drive
  per-NPC RNG streams via seed + npc_id + stream_id derivation
  (stream 0=init, stream 1=wander)
- Add get_wander_offset(npc_id) to SimulationManager so wander targets
  are deterministic per seed; WorldViewManager calls it instead of
  local randf_range()
- Add get_state_snapshot() and get_state_checksum() to SimulationManager
  for headless verification and future save/load
- Convert SimNPC/SimVillage const DEBUG_LOGS to instance var debug_logs
  so headless tests can silence output without recompilation
- Pass RandomNumberGenerator through SimNPC._init() instead of using
  global randf_range() for hunger/energy/position/scoring noise
- Remove obsolete farm_zone and forest_zone exports from
  WorldViewManager and their marker/tree scene children from main.tscn;
  NPC gather tasks use ResourceNode exclusively
- Rename TaskZone container to ActivityMarkers in main.tscn and update
  all scene paths (player, WVM, tests) to match
- Add headless deterministic_simulation_test.gd: verifies clock
  accuracy, same-seed equality, different-seed divergence, and
  24-tick scenario checksum without loading main.tscn

tests/deterministic_simulation_test.gd

@@ -0,0 +1,52 @@
+extends SceneTree
+
+var failures: Array[String] = []
+
+func _initialize() -> void:
+	call_deferred("_run")
+
+func _run() -> void:
+	var clock := SimulationClock.new(1.0)
+	_check(clock.advance(0.4) == 0, "Clock should not tick before its interval")
+	_check(clock.advance(0.6) == 1, "Clock should emit one tick at its interval")
+	_check(clock.advance(2.4) == 2, "Clock should preserve remainder across multiple ticks")
+	_check(clock.elapsed_ticks == 3, "Clock should track elapsed simulation ticks")
+
+	var first := _run_scenario(424242)
+	var second := _run_scenario(424242)
+	var different := _run_scenario(424243)
+
+	_check(first == second, "The same seed and commands should produce the same checksum")
+	_check(first != different, "A different seed should change the scenario checksum")
+
+	if failures.is_empty():
+		print("[TEST] Deterministic simulation passed | checksum=", first)
+		quit(0)
+		return
+
+	for failure in failures:
+		push_error("[TEST] " + failure)
+	quit(1)
+
+func _run_scenario(seed_value: int) -> String:
+	var manager: Node = load("res://simulation/SimulationManager.gd").new()
+	manager.simulation_seed = seed_value
+	manager.debug_logs = false
+	root.add_child(manager)
+	manager.set_process(false)
+
+	for step in 24:
+		manager.simulate_tick()
+		for npc in manager.npcs:
+			if npc.task_state == SimNPC.TASK_STATE_TRAVELING:
+				manager.notify_npc_arrived(npc.id)
+
+	var snapshot: Dictionary = manager.get_state_snapshot()
+	snapshot.erase("seed")
+	var checksum := JSON.stringify(snapshot).sha256_text()
+	manager.free()
+	return checksum
+
+func _check(condition: bool, message: String) -> void:
+	if not condition:
+		failures.append(message)

tests/deterministic_simulation_test.gd.uid

@@ -0,0 +1 @@
+uid://bexyksljoddd0

tests/flat_map_baseline_test.gd

@@ -28,10 +28,10 @@ func _run() -> void:
 	]
 	var destinations: Array[Vector3] = []
 	for marker_path in [
-		"TaskZone/FoodZone",
-		"TaskZone/GuardZone",
-		"TaskZone/StudyZone",
-		"TaskZone/RestZone"
+		"ActivityMarkers/FoodZone",
+		"ActivityMarkers/GuardZone",
+		"ActivityMarkers/StudyZone",
+		"ActivityMarkers/RestZone"
 	]:
 		destinations.append(main_scene.get_node(marker_path).global_position)