Gas burner building and the energy resource (#54)

A new building that consumes gas to produce energy, a new resource
stored and moved exactly like ore and gas.

The resource: EnergyResourceGlyph (a cell/bolt mark) + energy's own
warm yellow-green ResourceDefinition, registered in
ResourceDefinitions.ORDER/DEFINITIONS and GameState.RESOURCE_ENERGY.
Inventory/ResourceBar/ResourceTransferList needed no changes - #49
already made them resource-agnostic, confirmed structurally in the
test rather than touched.

The building: GasBurnerBuildingVisual (a hexagonal chamber with intake
vents in gas's colour and output ports in energy's, so the silhouette
itself reads "gas in, energy out"), GasBurnerBuildingDefinition
(capabilities=["gas_burner"], its own build-menu icon appended to
IconButton.Icon rather than inserted, per the ticket's own warning
about renumbering stored scene values), and the matching
UI/BuildMenu/GasBurner* nodes in Main.tscn. Gated behind a new
"Power Systems" skill-tree node, mirroring how "freight" unlocks the
transport hub.

Conversion: _advance_gas_burners(), simulated in GameState alongside
_advance_production/extractor mining so it keeps running while the
player is elsewhere. Withdraws gas and deposits energy in the
building's OWN inventory only - never the bank - so it stalls with no
local gas exactly like a lab waiting on materials.

Logistics: a gas burner's ongoing gas deficit is folded into the
existing queued-building-supply dispatch path (same "needs resource X"
loop production/research orders already use, extended with
gas_burner_gas_deficit()), and a new TO_BUILDING_PICKUP/
TO_MOTHERSHIP_FROM_BUILDING transporter state pair collects its energy
to the bank, mirroring the extractor pickup path per the ticket. The
existing f5c60f8 priority (queued deliveries outrank collection) holds:
the pickup dispatch loop runs last.

Tests: new tests/test_gas_burner.gd (resource genericity, stall
semantics, research gate, and full delivery+pickup logistics via a
real hub), run_tests transporter/resource regressions, and screenshots
of the build menu (all 7 buildings) and transfer menu (all 3
resources). Full suite: 81/81.

Two real bugs found and fixed along the way, neither gas-burner-
specific:
- _transporter_inbound_to() matched ANY non-idle transporter with a
  matching target_id, regardless of purpose. Once pickup states shared
  target_id with delivery states (both address a building, not an
  extractor), a transporter delivering gas made the SAME building look
  "busy" to the unrelated energy-pickup dispatch, starving it even
  with a second, genuinely free transporter sitting idle at the hub.
  Split into _transporter_inbound_to() (delivery states only) and a
  new _transporter_inbound_for_pickup() (pickup states only).
- The build menu's 3-row/6-slot layout (MENU_ROW_TOPS + row content
  sizing) had no room for a 7th building - despite the ticket's own
  note that no layout changes should be needed. A naive 4th row ran
  off the bottom of a 720x1280 viewport; fitting one meant both adding
  a 4th row top AND shrinking the shared button/label/cost sizing so
  each row's content no longer taller than the compressed row spacing.
  Caught only by actually screenshotting it - a real build menu, not
  headless, since --headless renders nothing.

🤖 Generated with Claude Code

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

BuildController.gd

@@ -490,14 +490,21 @@ func _planet_under_fleet() -> Node2D:
 # Grid geometry, shared with the layout below. Rows of two, and the menu is
 # rebuilt from whatever is currently researched (#21) rather than being a
 # fixed arrangement with holes punched in it.
-const MENU_ROW_TOPS: Array = [-300.0, -10.0, 280.0]
+const MENU_ROW_TOPS: Array = [-300.0, -77.0, 146.0, 369.0]
 const MENU_COL_X: float = 140.0
 const MENU_BUTTON_HALF: float = 64.0
-const MENU_BUTTON_H: float = 128.0
+const MENU_BUTTON_H: float = 100.0
 const MENU_LABEL_HALF: float = 150.0
-const MENU_LABEL_H: float = 66.0
+const MENU_LABEL_H: float = 52.0
 const MENU_COST_HALF: float = 60.0
-const MENU_COST_H: float = 52.0
+const MENU_COST_H: float = 44.0
+# Gaps from each row's own top to where the label/cost start, sized to the
+# shrunk MENU_*_H values above (#54: fitting a 4th row meant tightening
+# MENU_ROW_TOPS' spacing to 223px, less than the original 256px a row's
+# button+label+cost needed - shrinking those closed the gap without
+# resorting to a scrollable menu).
+const MENU_LABEL_OFFSET: float = 106.0
+const MENU_COST_OFFSET: float = 162.0
 
 
 func _place_entry(node: Control, cx: float, top: float, half: float, height: float) -> void:
@@ -530,8 +537,8 @@ func _layout_build_menu() -> void:
 		var cx: float = 0.0 if alone else (-MENU_COL_X if i % 2 == 0 else MENU_COL_X)
 		var top: float = MENU_ROW_TOPS[mini(row, MENU_ROW_TOPS.size() - 1)]
 		_place_entry(shown[i][1], cx, top, MENU_BUTTON_HALF, MENU_BUTTON_H)
-		_place_entry(shown[i][2], cx, top + 134.0, MENU_LABEL_HALF, MENU_LABEL_H)
-		_place_entry(shown[i][3], cx, top + 204.0, MENU_COST_HALF, MENU_COST_H)
+		_place_entry(shown[i][2], cx, top + MENU_LABEL_OFFSET, MENU_LABEL_HALF, MENU_LABEL_H)
+		_place_entry(shown[i][3], cx, top + MENU_COST_OFFSET, MENU_COST_HALF, MENU_COST_H)
 
 
 func _refresh_build_status() -> void: