#138: structures and doctrines cost more than rocks, and more the deeper they are

Both halves of the ticket, in the shape vessels have used since gas bombers
and laser ships: a definition carries an ore figure and, when it wants more
than ore, a dictionary that IS the price. `building_costs()` and
`skill_costs()` answer it the way `product_costs()` already did, so there is
one question with one answer whatever is being bought, and every payment
path now goes through `spend_resources` rather than `spend`.

Seven of ten structures and thirteen of seventeen doctrines now want gas,
energy or dark matter alongside their rocks, and the totals climb with tree
depth - structures 16/31/58/62/96 by depth, doctrines 15/30/73/96/143/258/530.

The constraint that shaped the table is REACHABILITY, and it is the reason
some prices stayed ore-only. Energy exists only where a gas burner stands,
and a gas burner needs Power Systems - so nothing at or before that depth
may be priced in energy, or it is a wall with no way through. Dark matter is
rarer still and appears once, on the deepest node in the game. The extractor
stays rocks-only despite its depth allowing gas, because the quest chain
reaches it before it has sent the player for any.

test_progressive_costs checks those as properties rather than transcribing
the numbers, so rebalancing a price costs nothing while breaking the shape
fails: nothing unreachable at its own depth, prices rising with depth, the
ore field agreeing with the dictionary (repairs quote the field alone, since
a repair drone carries ore and nothing else), and the quest chain never
asking for a structure it has not funded.

Two things cleaned up on the way:

- The per-building cost constants in GameState are gone. Nothing but tests
  used them, and they were a second copy of a number the definitions already
  hold - exactly what would drift once a price gained a resource.
- research_for_building() returns a display NAME, and the id-keyed half of
  the tree wants an id. That mix-up is silent - skill_depth() of a name finds
  no node and answers 0, so a deep structure reads as an ungated one, which
  is how the first draft of the test let an unreachable price through.
  research_node_for_building() is the id, and the name is expressed from it.

PriceTag no longer rebuilds its labels when re-told the same price; it
refreshes the held figures instead. The craft menu re-states prices every
frame and the build menu now does too, so that was a dozen Labels being torn
down and rebuilt sixty times a second.

ui/PriceTag.gd

@@ -47,6 +47,13 @@ const POINT_MARK: String = "RP"
 @export var show_available: bool = true
 
 var _entries: Array = []
+# The price currently on show. Kept so a caller that re-states the same price
+# every frame - the craft menu does, and since #138 the build menu does too -
+# refreshes the HELD figures instead of tearing down and rebuilding a dozen
+# Labels sixty times a second.
+var _shown_costs: Dictionary = {}
+var _shown_points: int = 0
+var _built: bool = false
 
 
 func _ready() -> void:
@@ -56,6 +63,13 @@ func _ready() -> void:
 
 # costs: {resource_type: amount}. points: research points, 0 for none.
 func show_price(costs: Dictionary, points: int = 0) -> void:
+	if _built and points == _shown_points and costs == _shown_costs:
+		# Same price, possibly a different wallet.
+		_refresh_held()
+		return
+	_shown_costs = costs.duplicate()
+	_shown_points = points
+	_built = true
 	_clear()
 	for resource_type in GameState.resource_types():
 		var amount: int = int(costs.get(resource_type, 0))
@@ -75,6 +89,29 @@ func set_costs(costs: Dictionary) -> void:
 	show_price(costs)
 
 
+# What the player holds, re-read. The price does not move; the wallet does.
+func _refresh_held() -> void:
+	var relayout: bool = false
+	for entry in _entries:
+		var have: int = GameState.research_points if String(entry.resource) == "" \
+			else GameState.available_resource(String(entry.resource))
+		if have == int(entry.have):
+			continue
+		entry.have = have
+		entry.short = have < int(entry.cost)
+		if entry.have_label == null:
+			continue
+		entry.have_label.text = "%d/" % have
+		entry.have_label.add_theme_color_override("font_color",
+			SHORT_COLOR if entry.short else HAVE_COLOR)
+		var width: float = _text_width(entry.have_label, HAVE_FONT_SIZE)
+		if not is_equal_approx(width, float(entry.have_width)):
+			entry.have_width = width
+			relayout = true
+	if relayout:
+		_layout()
+
+
 func is_free() -> bool:
 	return _entries.is_empty()