feat: TimeSystem 增加月/年信号与日期设置接口

- 新增 month_passed/year_passed 信号，供俸禄与年度结算
- 新增 speed_changed/pause_changed 信号及 set_paused
- 新增 set_date 接口，供读档恢复时间

src/Core/TimeSystem.gd

@@ -1,6 +1,10 @@
 extends Node
 
 signal day_passed(year, month, day)
+signal month_passed(year, month)
+signal year_passed(year)
+signal speed_changed(speed_index)
+signal pause_changed(paused)
 
 const SPEEDS := [1.0, 5.0, 20.0]
 const DAYS_PER_MONTH := 30
@@ -25,28 +29,45 @@ func _is_in_game() -> bool:
 	return scene != null and scene.name == "MainGame"
 
 func _advance() -> void:
+	var new_month := false
+	var new_year := false
 	GameState.day += 1
 	if GameState.day > DAYS_PER_MONTH:
 		GameState.day = 1
 		GameState.month += 1
+		new_month = true
 		if GameState.month > MONTHS_PER_YEAR:
 			GameState.month = 1
 			GameState.year += 1
+			new_year = true
 	day_passed.emit(GameState.year, GameState.month, GameState.day)
+	if new_month:
+		month_passed.emit(GameState.year, GameState.month)
+	if new_year:
+		year_passed.emit(GameState.year)
 
 func cycle_speed() -> float:
 	speed_index = (speed_index + 1) % SPEEDS.size()
 	speed = SPEEDS[speed_index]
+	speed_changed.emit(speed_index)
 	return speed
 
 func set_speed_index(index: int) -> void:
 	speed_index = clampi(index, 0, SPEEDS.size() - 1)
 	speed = SPEEDS[speed_index]
+	speed_changed.emit(speed_index)
 
 func toggle_pause() -> bool:
 	paused = not paused
+	pause_changed.emit(paused)
 	return paused
 
+func set_paused(value: bool) -> void:
+	if paused == value:
+		return
+	paused = value
+	pause_changed.emit(paused)
+
 func get_speed_label() -> String:
 	return "x%d" % int(speed)
 
@@ -55,3 +76,8 @@ func get_current_date() -> Array:
 
 func get_date_text() -> String:
 	return "%d年 %d月 %d日" % [GameState.year, GameState.month, GameState.day]
+
+func set_date(y: int, m: int, d: int) -> void:
+	GameState.year = y
+	GameState.month = m
+	GameState.day = d