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/test_joystick_control.gd

@@ -120,9 +120,17 @@ func _process(delta: float) -> bool:
 			for ship in fleet.ships:
 				speed = max(speed, ship.velocity.length())
 			var stopped: bool = speed < 1.0
-			var coasted: bool = fleet.get_centroid().x > moving_centroid.x
-			print("after release: max_speed=%.3f stopped=%s coasted_further=%s" % [
-				speed, stopped, coasted
+			# Not merely "moved forward at all": the fleet cruises at
+			# cruise_speed and brakes at Ship.acceleration, so the coast is
+			# cruise_speed^2 / (2 * acceleration) ~ 75 units. Asserting a
+			# real distance is what makes this a test of coasting - the old
+			# `> moving_centroid.x` was satisfied by any float wobble, and
+			# passed happily while the fleet stopped dead.
+			var coast: float = fleet.get_centroid().x - moving_centroid.x
+			var coasted: bool = coast > 40.0
+			print("after release: max_speed=%.3f stopped=%s coasted=%.1f units (expected ~%.0f)" % [
+				speed, stopped, coast,
+				(fleet.cruise_speed * fleet.cruise_speed) / (2.0 * fleet.ships[0].acceleration)
 			])
 			if stopped and coasted:
 				print("TEST_JOYSTICK_CONTROL: PASS")