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

simulation/SimNPC.gd

@@ -1,8 +1,6 @@
 class_name SimNPC
 extends RefCounted
 
-const DEBUG_LOGS := true
-
 const TASK_STATE_IDLE := "idle"
 const TASK_STATE_TRAVELING := "traveling"
 const TASK_STATE_WORKING := "working"
@@ -29,22 +27,33 @@ var task_progress := 0.0
 var task_complete := true
 var target_id: StringName = &""
 var last_task := ""
+var random_source: RandomNumberGenerator
+var debug_logs := true
 
 func _init(
 	_id: int,
 	_npc_name: String,
 	_profession: String,
 	_strength: float,
-	_intelligence: float
+	_intelligence: float,
+	_random_source: RandomNumberGenerator = null
 ) -> void:
 	id = _id
 	npc_name = _npc_name
 	profession = _profession
 	strength = _strength
 	intelligence = _intelligence
-	hunger = randf_range(20.0, 80.0)
-	energy = randf_range(40.0, 100.0)
-	position = Vector3(randf_range(-8.0, 8.0), 0.0, randf_range(-8.0, 8.0))
+	random_source = _random_source
+	if random_source == null:
+		random_source = RandomNumberGenerator.new()
+		random_source.seed = id + 1
+	hunger = random_source.randf_range(20.0, 80.0)
+	energy = random_source.randf_range(40.0, 100.0)
+	position = Vector3(
+		random_source.randf_range(-8.0, 8.0),
+		0.0,
+		random_source.randf_range(-8.0, 8.0)
+	)
 
 func simulate_tick(village: SimVillage) -> void:
 	if is_dead:
@@ -104,7 +113,7 @@ func die_from_starvation() -> void:
 	task_duration = 0.0
 	task_complete = true
 
-	if DEBUG_LOGS:
+	if debug_logs:
 		print("[SimNPC] ", npc_name, " died from starvation.")
 		
 func choose_new_task(village: SimVillage) -> void:
@@ -231,9 +240,9 @@ func calculate_task_score(
 	if task_name == last_task:
 		score -= 1.5
 
-	score += randf_range(0.0, 0.5)
+	score += random_source.randf_range(0.0, 0.5)
 
-	if DEBUG_LOGS:
+	if debug_logs:
 		print(
 			"[SimNPC] ",
 			npc_name,