Share one backdrop between game and editor, and fix three input/economy bugs

The setup editor and the landed surface drew different backgrounds for the
same planet. Each scene carried its own hand-written ShaderMaterial, and only
the game side ever swapped in a profile's shader, so a gas giant authored in
the editor showed recoloured craters while the game showed cloud bands. Both
now instance one SurfaceBackground.tscn and configure it through one method,
and every profile names its own shader - the old "null means keep whatever
the scene already had" convention was the drift, since each scene "already
had" something different. The shared material is resource_local_to_scene, or
two live surfaces would repaint each other.

The gas giant's bands broke into disjoint segments once per cell: the second
turbulence octave doubled only the INTEGER half of a lattice coordinate,
which is a different point in every cell rather than the same point at twice
the frequency. Measured, the old form steps 0.153 at a cell boundary against
0.0002 now. A second discontinuity went with it - the camera cell index
arrives pre-wrapped, so hashing it raw rearranged the whole sky every 32
cells; hashes are now wrapped per octave and the field is exactly periodic.
Bands also gained low-frequency octaves and per-row differential drift.

WorldMap swallowed every touch in _input(), which runs before the GUI system,
so CloseButton never saw one: the map could be opened and not closed. Android
and desktop hid it behind Godot's emulated mouse event, which this never
swallowed; a phone browser gives no such second chance. Its test had been
closing the map by calling the method the button was failing to reach.

Construction now draws on the fleet hold as well as the bank. With an empty
starting bank and ore bankable only at a mothership, charging construction to
the bank alone made the first mothership cost ore that could not yet exist.

Also: a conquered planet no longer re-spawns its garrison (guarded on having
capture points, since a setup with none registers as vacuously conquered);
planets keep the map they drew, with the candidate list sorted rather than
left in filesystem order and assignments pruned rather than cleared on
rescan; and the map editor lists setups at a tappable size and can delete
one, as an explicit armed mode rather than a tap away from destroying work.

Full suite 106/106.

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

GameState.gd

@@ -1816,3 +1816,39 @@ func spend(cost: int) -> bool:
 		return false
 	bank_inventory.withdraw(RESOURCE_ORE, cost)
 	return true
+
+
+# --- construction: the bank AND what the ships are carrying -----------------
+#
+# A build is put up by the fleet, on the spot, so it can use ore the fleet is
+# holding as well as ore already banked. That is not a convenience: a fresh
+# game starts with an empty bank, and the ONLY way to bank ore is to deliver
+# it to a mothership. Charging construction to the bank alone therefore made
+# the first mothership cost ore that could not exist yet - the fleet could
+# mine all it liked and the game was unwinnable.
+#
+# Research still spends from the bank alone (can_afford/spend above). That
+# stays deliberate: hauling ore back to a base to fund science is the loop,
+# and unlike construction it was never deadlocked, because by the time there
+# is anything to research there is a mothership to bank into.
+
+
+func construction_ore() -> int:
+	return bank_inventory.amount(RESOURCE_ORE) + fleet_inventory.amount(RESOURCE_ORE)
+
+
+func can_afford_construction(cost: int) -> bool:
+	return construction_ore() >= cost
+
+
+func spend_construction(cost: int) -> bool:
+	# Bank first, hold second. The hold is also the fleet's mining capacity,
+	# so leaving it as full as possible means the next trip out can still
+	# carry something back.
+	if not can_afford_construction(cost):
+		return false
+	var from_bank: int = bank_inventory.withdraw(RESOURCE_ORE, cost)
+	var remaining: int = cost - from_bank
+	if remaining > 0:
+		fleet_inventory.withdraw(RESOURCE_ORE, remaining)
+	return true