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>

AsteroidExplosionVFX.gd

@@ -17,13 +17,21 @@ func _random_particle_size() -> float:
 	return randf_range(3.0, 7.0)
 
 
-func _draw_particle(p: Dictionary, alpha: float) -> void:
+# Debris tumbles independently of its flight path, unlike the light-burst
+# streaks - each chunk needs its own evolving rotation, so the base class
+# must keep writing visual.rotation every frame instead of leaving it fixed.
+func _particle_spins() -> bool:
+	return true
+
+
+func _configure_particle(visual: ExplosionParticle, p: Dictionary) -> void:
 	var s: float = p["size"]
+	# Unrotated local points - the child node's own `rotation` (driven by
+	# the base class from p["rot"]) supplies the tumble that used to be
+	# baked into a fresh pt.rotated(p["rot"]) call every frame.
 	var local_pts: PackedVector2Array = PackedVector2Array([
 		Vector2(-s, -s * 0.6), Vector2(s * 0.7, -s * 0.5),
 		Vector2(s, s * 0.5), Vector2(-s * 0.6, s),
 	])
-	var world_pts: PackedVector2Array = PackedVector2Array()
-	for pt in local_pts:
-		world_pts.append(p["pos"] + pt.rotated(p["rot"]))
-	draw_colored_polygon(world_pts, Color(COLOR.r, COLOR.g, COLOR.b, alpha))
+	visual.draw_callable = func(item: CanvasItem) -> void:
+		item.draw_colored_polygon(local_pts, COLOR)