Transport Hub building

Forgejo #18, part 5 of #12. The building only - the vessels that do the
hauling are #19. Placeable, costed at 30, gated behind a new "Freight
Handling" research node hanging off Logistics, with its own info popup,
build-menu glyph and map marker.

Drawn as an octagonal dock ring with berth arms and a squared-off freight
core: deliberately radial-but-flat so it does not read as a small
mothership, which is the only structure with swept arms. Its stationed
transports are NeonPiece children of one rotating holder, per #10 - the
geometry is rasterised once and only the holder's rotation changes, so
the traffic costs no redraws.

Building._draw()'s match has a catch-all that renders anything
unrecognised as a ship crafter, so a missing case is silent and looks
almost right. The test checks for the hub's own _hub_traffic holder
rather than trusting that something plausible appeared - which caught
exactly that: a _ready() patch had silently not applied and the hub was
rendering through the crafter branch.

The build menu grew a third row. Every button, label and price moved:
the old row occupied 332px against a 372px pitch, and three of those do
not fit above a 1280px screen. Rows are now shorter (128px buttons, 40px
price digits) at a 290px pitch, ending at y=1176. Rendered and looked at
- the first attempt tightened the pitch alone and left every price
overlapping the row beneath it, which no headless test would have seen.

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

IconButton.gd

@@ -15,7 +15,7 @@ enum Icon {
 	# build menu used to pick from the generic set, which left the mothership
 	# and the command centre sharing a folded-map glyph and neither of them
 	# looking anything like the structure they build.
-	MOTHERSHIP, CRAFTER, COMMAND_CENTER, EXTRACTOR,
+	MOTHERSHIP, CRAFTER, COMMAND_CENTER, EXTRACTOR, TRANSPORT_HUB,
 }
 
 # Size the glyphs were originally drawn against. Every glyph dimension is
@@ -119,6 +119,8 @@ func _draw() -> void:
 			_draw_command_icon(center, pulse, s)
 		Icon.EXTRACTOR:
 			_draw_extractor_icon(center, pulse, s)
+		Icon.TRANSPORT_HUB:
+			_draw_transport_hub_icon(center, pulse, s)
 
 
 func _draw_close(center: Vector2, pulse: float, s: float) -> void:
@@ -204,6 +206,32 @@ func _draw_mothership_icon(center: Vector2, pulse: float, s: float) -> void:
 		NeonDraw.draw_glowing_polygon(self, ring, _active_color(), pulse, core_color)
 
 
+func _draw_transport_hub_icon(center: Vector2, pulse: float, s: float) -> void:
+	# A ring of docking cradles with a freight box in the middle: reads as
+	# "things are stationed here and go out from here", which is what the hub
+	# does, and shares no silhouette with the crafter's open cradle.
+	var ring_r: float = 11.0 * s
+	var ring: PackedVector2Array = PackedVector2Array()
+	for i in range(8):
+		var a: float = (float(i) / 8.0) * TAU + PI / 8.0
+		ring.append(center + Vector2(cos(a), sin(a)) * ring_r)
+	NeonDraw.draw_glowing_polygon(self, ring, _active_color(), pulse, core_color)
+
+	var box: float = 4.2 * s
+	NeonDraw.draw_glowing_polygon(self, PackedVector2Array([
+		center + Vector2(-box, -box), center + Vector2(box, -box),
+		center + Vector2(box, box), center + Vector2(-box, box),
+	]), _active_color(), pulse, core_color)
+
+	# Three stubby berths, so the ring reads as occupied rather than as a
+	# plain octagon.
+	for i in range(3):
+		var a: float = (float(i) / 3.0) * TAU - PI / 2.0
+		var dir: Vector2 = Vector2(cos(a), sin(a))
+		NeonDraw.draw_glowing_line(self, center + dir * (box * 1.5),
+			center + dir * (ring_r - 1.5 * s), _active_color(), pulse, 0.35 * s, core_color)
+
+
 func _draw_crafter_icon(center: Vector2, pulse: float, s: float) -> void:
 	# Reactor core, truss spine, and an open cradle holding a hull.
 	var core_centre: Vector2 = center + Vector2(-11, 0) * s