Skill tree, node-based building animation, bigger UI, and a 19x faster test suite

Gameplay and UI
- Research tree at the mothership gates which structures can be built and
  grants permanent fleet-capacity upgrades (GameState.SKILL_TREE,
  SkillTreeView). Node depth is derived from prerequisites, so the layout
  cannot drift out of step with the dependencies.
- Building info popup before committing to a build, with per-building cost
  and description.
- Ship crafter redrawn as a space factory with an assembly animation;
  mothership redrawn as a radial flagship; command centre as a plotting hub.
- Keyboard and mouse support (WASD, Q/E pivot, wheel zoom) for the web build.
- UI and font scaled up for phone use, via a custom Theme resource -
  gui/theme/default_font_size does not reach the default theme.
- Asteroids no longer spawn on top of the fleet's start position.
- Fleet formation origin derived from the layout's own offsets rather than
  the centroid, fixing the lurch when a lopsided formation started moving.
- Fleet.stop() brakes from the ship's TRUE motion (velocity +
  fleet_velocity). Ship zeroes its velocity when seated in its slot even
  while the anchor drags that slot forward, so braking from velocity alone
  stopped the fleet dead instead of coasting - and whether it did depended
  on the frame rate.

Animation architecture (issue #10)
- Buildings, projectiles and explosion VFX no longer animate by redrawing.
  Static geometry is rasterised once in _draw(); moving parts are NeonPiece
  children animated through node properties, which reuse the cached
  geometry. Every NeonDraw call expands into four antialiased polylines, so
  redrawing to move something re-tessellated all of it.

Test suite (issue #8): 1075s -> ~55s
- Runs from a copy on Termux's own filesystem. The project lives on
  Android's FUSE bridge, read through proot, where load("res://Main.tscn")
  alone cost 8.5s per test against ~2s natively - and nearly every test
  loads it.
- Runs 6 tests at a time, in a single proot-distro login, with output
  buffered per test and printed only on failure.
- --fixed-fps 60 pins delta instead of measuring the wall clock, so a test's
  result no longer depends on how busy the machine is. Without it,
  parallelism made two tests fail on 2 of 3 runs.
- A test passes only if it both exits 0 and prints ": PASS".
- 38 tests, green on three consecutive runs.

Bundles Carrois Gothic SC (Apache 2.0) with its licence text.

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

Fleet.gd

@@ -39,7 +39,7 @@ func spawn_ships(count: int, center: Vector2 = Vector2.ZERO) -> void:
 	ships.clear()
 	formation_offsets.clear()
 
-	var n: int = clamp(count, 1, GameState.formation.size())
+	var n: int = clamp(count, 1, GameState.max_fleet_size())
 	for i in range(n):
 		var offset: Vector2 = GameState.formation[i]
 		var ship: Area2D = ship_scene.instantiate()
@@ -58,7 +58,7 @@ func spawn_ships(count: int, center: Vector2 = Vector2.ZERO) -> void:
 func add_ship() -> bool:
 	# Adds one vessel in the next free formation slot (bought from a ship
 	# crafter). Returns false when the wedge is already full.
-	if ships.size() >= GameState.formation.size():
+	if ships.size() >= GameState.max_fleet_size():
 		return false
 	var offset: Vector2 = GameState.formation[ships.size()]
 	var ship: Area2D = ship_scene.instantiate()
@@ -82,7 +82,7 @@ func apply_formation() -> void:
 	# Without this, editing the layout at a command centre (or pivoting it)
 	# only affected ships built later, which read as the edit doing nothing.
 	for i in range(ships.size()):
-		if i >= GameState.formation.size():
+		if i >= GameState.max_fleet_size():
 			break
 		formation_offsets[i] = GameState.formation[i]
 	_assign_slot_targets()
@@ -138,12 +138,32 @@ func stop() -> void:
 	# since that lands inside arrive_radius immediately).
 	fleet_target = get_formation_origin()
 	for ship in ships:
-		var speed: float = ship.velocity.length()
+		# A ship's own `velocity` is NOT how fast it is really travelling
+		# while the fleet cruises. Ship snaps to its slot and reports zero
+		# the moment it is within arrive_radius of it, even though the
+		# anchor is dragging that slot forward at cruise_speed underneath
+		# it. Its true motion is its catch-up velocity PLUS the fleet's,
+		# which it already carries as `fleet_velocity` (zero for a
+		# point-to-point move_to, where `velocity` alone is the whole
+		# story).
+		#
+		# Braking from `velocity` alone therefore stopped the fleet dead
+		# on any frame where the ships happened to be seated - and how
+		# often that happens depends on the frame rate, because the anchor
+		# advances cruise_speed * delta per frame. At ~25fps it steps far
+		# enough that ships always lag and always report motion, which is
+		# the only reason releasing the stick looked right.
+		var motion: Vector2 = ship.velocity + ship.fleet_velocity
+		# Context that is no longer true: the fleet is not cruising any
+		# more, so leaving it set would have Ship face a heading it is not
+		# travelling on.
+		ship.fleet_velocity = Vector2.ZERO
+		var speed: float = motion.length()
 		if speed <= 0.001:
 			ship.set_move_target(ship.position)
 			continue
 		var braking_distance: float = (speed * speed) / (2.0 * ship.acceleration)
-		ship.set_move_target(ship.position + ship.velocity.normalized() * braking_distance)
+		ship.set_move_target(ship.position + motion.normalized() * braking_distance)
 
 
 func get_move_targets() -> Array: