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>

tests/_vfx_preview.gd

@@ -0,0 +1,47 @@
+extends Node2D
+
+# Preview scene - NOT run by run_tests.sh (underscore prefix). Renders
+# projectiles and every explosion type so the node-animation conversion
+# (issue #10) can be checked by eye. Bolts once went INVISIBLE after a
+# similar optimisation and headless tests did not catch it, because
+# --headless has no GPU - so this exists to make that failure visible.
+#
+#   bash tests/screenshot.sh res://tests/_vfx_preview.tscn out.png 20
+
+const VFX_SCRIPTS: Array = [
+	"res://ShipExplosionVFX.gd", "res://EnemyExplosionVFX.gd",
+	"res://AsteroidExplosionVFX.gd", "res://LightBurstVFX.gd",
+]
+
+
+func _ready() -> void:
+	RenderingServer.set_default_clear_color(Color(0.02, 0.03, 0.06))
+
+	# Bolts at several headings, held still so they can be inspected.
+	var bolt_scene: PackedScene = load("res://Projectile.tscn")
+	for i in range(6):
+		var bolt: Area2D = bolt_scene.instantiate()
+		bolt.position = Vector2(-460.0 + float(i) * 90.0, -220.0)
+		bolt.rotation = float(i) * 0.35
+		add_child(bolt)
+		bolt.set_physics_process(false)
+
+	# One of each explosion, stepped forward by hand then frozen. Their real
+	# lifetime is under a second, and a softpipe frame takes far longer than
+	# that in wall-clock, so they would expire before the capture.
+	for i in range(VFX_SCRIPTS.size()):
+		var script: Script = load(VFX_SCRIPTS[i])
+		if script == null:
+			continue
+		var vfx: Node2D = Node2D.new()
+		vfx.set_script(script)
+		vfx.position = Vector2(-390.0 + float(i) * 260.0, 90.0)
+		vfx.lifetime = 999.0
+		add_child(vfx)
+		for step in range(8):
+			vfx._process(0.05)
+		vfx.set_process(false)
+
+	var cam: Camera2D = Camera2D.new()
+	add_child(cam)
+	cam.make_current()