Buy fleet berths with Fleet Offices

#219: fleet capacity is a built, supplied thing rather than a researched
one. The eight fleet-size doctrines are gone; capacity is one berth free
plus one per Fleet Office standing. An office charges every 25s for the
vessel in its berth, priced off that vessel's own build cost so an expensive
hull is expensive to keep, and drawn from its own store the way a gas burner
draws gas. An office that cannot pay goes dark, its vessel is scuttled, and
the player is told through the same queue quest lines use - which reaches
them on a planet surface too.

An empty berth is idle rather than starved: an office is only failing while
there is something in it to fail, and holding it disabled would leave a
berth that could never be crewed and so could never be paid for again.

Ships have no hit points and a shield absorbs a hit wholesale, so the lost
vessel is scuttled rather than damaged - otherwise a shielded hull would
survive its own eviction.

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

tests/test_skill_menu.gd

@@ -126,6 +126,18 @@ func _process(delta: float) -> bool:
 	print("a second click on the same node researches it")
 
 	# --- C. held drag scrolls, a bare hover does not --------------------
+	# #219 removed the eight-deep doctrine lane and the tree now fits its own
+	# view, so there is nothing left to scroll. What is under test here is the
+	# INPUT rule - drag only while the button is held, wheel both ways - not
+	# how tall the tree happens to be, so the view is shortened to give the
+	# gesture something to move. Scrolled to the bottom first, the way the
+	# menu opens when the content does overflow.
+	var authored_height: float = tree_view.size.y
+	tree_view.size.y = authored_height * 0.4
+	tree_view.scroll_y = tree_view._max_scroll()
+	if tree_view.scroll_y <= 0.0:
+		return _fail("the tree still has nothing to scroll, so this proves nothing")
+
 	var before: float = tree_view.scroll_y
 	_move(Vector2(0.0, 120.0))
 	if not is_equal_approx(tree_view.scroll_y, before):
@@ -153,6 +165,10 @@ func _process(delta: float) -> bool:
 	print("the wheel scrolls both ways")
 
 	# --- E. the panel has no dead band at the bottom --------------------
+	# Back to the authored height: section C shortened the view to have
+	# something to scroll, and the layout below is about the real one.
+	tree_view.size.y = authored_height
+	tree_view.scroll_y = 0.0
 	var detail: Control = scene.get_node("UI/SkillMenu/DetailLabel")
 	var status: Control = scene.get_node("UI/SkillMenu/StatusLabel")
 	var tree_bottom: float = tree_view.position.y + tree_view.size.y