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>

PlanetSurface.tscn

@@ -58,10 +58,10 @@ layer = 1
 mouse_filter = 2
 offset_left = 28
 offset_top = 24
-offset_right = 520
-offset_bottom = 140
+offset_right = 320
+offset_bottom = 92
 script = ExtResource("9")
-digit_height = 100.0
+digit_height = 60.0
 glow_color = Color(0, 0.42, 0.48, 1)
 core_color = Color(0, 0.08, 0.1, 1)
 
@@ -143,22 +143,6 @@ icon = 6
 glow_color = Color(0.06, 0.32, 0.5, 1)
 core_color = Color(0.02, 0.09, 0.15, 1)
 
-[node name="NavLabel" type="Label" parent="UI"]
-mouse_filter = 2
-anchor_left = 1.0
-anchor_right = 1.0
-anchor_top = 1.0
-anchor_bottom = 1.0
-offset_left = -344
-offset_right = -24
-offset_top = -322
-offset_bottom = -196
-text = "Pivot"
-theme_override_colors/font_color = Color(0.08, 0.08, 0.11, 1)
-theme_override_colors/font_outline_color = Color(0.95, 0.95, 0.96, 0.85)
-theme_override_constants/outline_size = 5
-horizontal_alignment = 1
-
 [node name="FadeOverlay" type="CanvasLayer" parent="."]
 layer = 10