Charge more for each berth, and show the bill

#220: every berth past the first paid one costs 1.12x the one before it, on
top of the flat per-vessel charge. A linear bill makes the tenth hull no more
of a decision than the second; compounding weighs each addition against the
whole fleet behind it. Shallow on purpose - the thirteenth berth costs about
three and a half times the second, the twentieth about seven and a half.

Fleet Offices gain a menu naming the whole bill per minute, a line per paying
berth with its multiplier, and the arithmetic in words. It renders
fleet_upkeep_breakdown(), which is the calculation the charging loop itself
runs: a readout that summed independently could quote a bill the game does
not take, which is the thing worth preventing here. The test pins that what
the menu quotes for a berth is what that office is charged.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019AJMdB7iuHuLFZM1aBu3GD

ui/menus/FleetUpkeepMenu.gd

@@ -0,0 +1,71 @@
+extends "res://ui/menus/ModalMenu.gd"
+
+# Forgejo #220: what the fleet costs to keep, and WHY it costs that.
+#
+# A Fleet Office charges for the vessel in its berth every 25 seconds, and
+# each berth costs more than the one before it. Neither of those is visible
+# from the resource bar - the player watches a number fall and cannot tell
+# which of their own decisions is draining it - so this states the bill and
+# shows the arithmetic that produced it, line by line.
+#
+# Every number here comes from GameState.fleet_upkeep_breakdown(), which is
+# the same calculation the charging loop runs. A readout that did its own sum
+# could disagree with what is actually being taken, which is exactly the kind
+# of "the game is lying to me" the ticket is about.
+
+@onready var total_label: Label = $TotalLabel
+@onready var detail_label: Label = $DetailLabel
+@onready var formula_label: Label = $FormulaLabel
+
+var building_id: int = 0
+
+
+func open_for(next_building_id: int) -> void:
+	building_id = next_building_id
+	open_menu()
+	refresh()
+
+
+func close_menu() -> void:
+	super.close_menu()
+	building_id = 0
+
+
+func refresh() -> void:
+	if not visible:
+		return
+	var breakdown: Dictionary = GameState.fleet_upkeep_breakdown()
+	var berths: Array = breakdown.berths
+	var per_minute: Dictionary = breakdown.per_minute
+
+	if per_minute.is_empty():
+		total_label.text = "NOTHING TO KEEP"
+	else:
+		var parts: PackedStringArray = PackedStringArray()
+		for resource_type in per_minute:
+			parts.append("%.1f %s" % [float(per_minute[resource_type]),
+				GameState.resource_name(String(resource_type)).to_lower()])
+		total_label.text = "%s PER MINUTE" % " · ".join(parts)
+
+	# One line per paying berth: which hull, what it is charged, and the
+	# multiplier that got it there. An empty berth is charged nothing and is
+	# left out rather than listed at zero.
+	var lines: PackedStringArray = PackedStringArray()
+	for berth in berths:
+		var costs: PackedStringArray = PackedStringArray()
+		for resource_type in berth.costs:
+			costs.append("%d %s" % [int(berth.costs[resource_type]),
+				GameState.resource_name(String(resource_type)).to_lower()])
+		lines.append("BERTH %d  %-16s %s  (x%.2f)%s" % [
+			int(berth.slot), GameState.vessel_name(String(berth.vessel_type)),
+			" ".join(costs), float(berth.scale),
+			"  — UNPAID" if bool(berth.starved) else "",
+		])
+	detail_label.text = "\n".join(lines) if not lines.is_empty() \
+		else "No berth is being charged. Build a Fleet Office and put a vessel in it."
+
+	formula_label.text = ("Each berth is charged every %ds: the vessel's build price "
+		+ "divided by %d, then multiplied by %.2f for every berth past the first "
+		+ "paid one. The first vessel is free.") % [
+			int(breakdown.charge_seconds), int(breakdown.divisor),
+			float(breakdown.growth)]

ui/menus/FleetUpkeepMenu.tscn

@@ -0,0 +1,77 @@
+[gd_scene load_steps=3 format=3]
+
+[ext_resource type="Script" path="res://ui/IconButton.gd" id="icon"]
+[ext_resource type="Script" path="res://ui/menus/FleetUpkeepMenu.gd" id="menu"]
+
+[node name="FleetUpkeepMenu" type="Control" groups=["modal_menus"]]
+visible = false
+mouse_filter = 2
+anchor_right = 1.0
+anchor_bottom = 1.0
+script = ExtResource("menu")
+
+[node name="Backdrop" type="ColorRect" parent="."]
+mouse_filter = 2
+anchor_right = 1.0
+anchor_bottom = 1.0
+color = Color(0.03, 0.03, 0.08, 0.96)
+
+[node name="TitleLabel" type="Label" parent="."]
+mouse_filter = 2
+anchor_right = 1.0
+offset_left = 24.0
+offset_top = 24.0
+offset_right = -180.0
+offset_bottom = 100.0
+theme_override_font_sizes/font_size = 40
+text = "FLEET UPKEEP"
+horizontal_alignment = 1
+
+[node name="CloseButton" type="Control" parent="."]
+anchor_left = 1.0
+anchor_right = 1.0
+offset_left = -140.0
+offset_top = 24.0
+offset_right = -24.0
+offset_bottom = 140.0
+script = ExtResource("icon")
+icon = 1
+glow_color = Color(0.55, 0.6, 1, 1)
+
+[node name="TotalLabel" type="Label" parent="."]
+mouse_filter = 2
+anchor_right = 1.0
+offset_left = 32.0
+offset_top = 150.0
+offset_right = -32.0
+offset_bottom = 220.0
+theme_override_font_sizes/font_size = 32
+theme_override_colors/font_color = Color(1, 0.85, 0.35, 1)
+text = ""
+horizontal_alignment = 1
+
+[node name="DetailLabel" type="Label" parent="."]
+mouse_filter = 2
+anchor_right = 1.0
+offset_left = 32.0
+offset_top = 250.0
+offset_right = -32.0
+offset_bottom = 860.0
+theme_override_font_sizes/font_size = 30
+theme_override_colors/font_color = Color(0.72, 0.88, 0.96, 1)
+text = ""
+autowrap_mode = 2
+
+[node name="FormulaLabel" type="Label" parent="."]
+mouse_filter = 2
+anchor_right = 1.0
+offset_left = 40.0
+offset_top = 880.0
+offset_right = -40.0
+offset_bottom = 1060.0
+theme_override_font_sizes/font_size = 26
+theme_override_colors/font_color = Color(0.55, 0.78, 0.86, 1)
+text = ""
+horizontal_alignment = 1
+vertical_alignment = 1
+autowrap_mode = 2