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>

NeonNumber.gd

@@ -16,6 +16,13 @@ extends Control
 @export var digit_height: float = 30.0
 @export var digit_gap: float = 9.0
 
+# Segment weight as a fraction of digit height, so the strokes keep the same
+# visual heft at any size. This used to be a fixed width regardless of the
+# digit height, which left large readouts looking hairline next to the solid
+# ore hexagon beside them.
+const STROKE_RATIO: float = 0.014
+const HEX_STROKE_RATIO: float = 0.030
+
 # Which of the seven segments each digit lights, in the usual order:
 # top, top-right, bottom-right, bottom, bottom-left, top-left, middle.
 const DIGIT_SEGMENTS: Array = [
@@ -60,8 +67,8 @@ func _draw_hexagon(centre: Vector2, radius: float) -> void:
 	for i in range(6):
 		var a: float = (float(i) / 6.0) * TAU - PI / 2.0
 		pts.append(centre + Vector2(cos(a), sin(a)) * radius)
-	NeonDraw.draw_glowing_polygon(self, pts, glow_color, 1.0, core_color)
-	NeonDraw.draw_glowing_line(self, pts[5], pts[2], glow_color, 0.6, 0.26, core_color)
+	NeonDraw.draw_glowing_polygon(self, pts, glow_color, 1.0, core_color, radius * HEX_STROKE_RATIO)
+	NeonDraw.draw_glowing_line(self, pts[5], pts[2], glow_color, 0.6, radius * HEX_STROKE_RATIO * 0.8, core_color)
 
 
 func _draw_digit(value: int, at: Vector2, w: float, h: float) -> void:
@@ -78,7 +85,8 @@ func _draw_digit(value: int, at: Vector2, w: float, h: float) -> void:
 		[Vector2(0.0, 0.0), Vector2(0.0, mid)],      # top-left
 		[Vector2(0.0, mid), Vector2(w, mid)],        # middle
 	]
+	var stroke: float = h * STROKE_RATIO
 	for i in range(seg.size()):
 		if not on[i]:
 			continue
-		NeonDraw.draw_glowing_line(self, at + seg[i][0], at + seg[i][1], glow_color, 1.0, 0.3, core_color)
+		NeonDraw.draw_glowing_line(self, at + seg[i][0], at + seg[i][1], glow_color, 1.0, stroke, core_color)