Add space-time distorder vessel and fleet speed fader (#59)

GameState.fleet_speed_multiplier (1.0-3.0) is applied at the point of
use - Fleet's cruise anchor and Ship's own max_speed/acceleration -
rather than baked into stored stats, so a stat upgrade researched
mid-boost can't corrupt the base value and the fader takes effect
immediately with no re-apply step.

Ship.arrive_radius is scaled by the same multiplier: at higher speeds
each physics tick covers a proportionally larger step, and once that
step outgrows a fixed arrive_radius the ship can overshoot its
snap-to-target zone every tick while chasing a target that's now also
receding faster - visible as the fleet stretching apart under boost.
Scaling it preserves the same "snaps onto its slot" tightness at any
boost level that 1.0x already has.

SpeedFader.gd is a self-contained vertical drag control (TouchJoystick's
raw-touch idiom, not _gui_input) that writes straight to the autoload
rather than reporting a value for something else to apply. It also
resets the multiplier to 1.0 the instant fleet.has_capability("distorder")
goes false, so a fleet can never be left permanently boosted by a vessel
it no longer has.

VesselDistorderComponent carries no per-shot behaviour (energy drain
while boosted is #62) - its presence is what matters. Registered in
VesselDefinitions, wired into the crafter/hangar/ship-lab menus per
#57's note (5/5/6 -> 6/6/7 columns).

VesselDistorderComponent.gd

@@ -0,0 +1,9 @@
+class_name VesselDistorderComponent
+extends Node
+
+# Pure presence marker (#59) - no per-shot behaviour, no tick(). Its only
+# job is to make Ship.has_capability("distorder") true, which is what
+# SpeedFader.gd/Fleet.gd key off to reveal and apply the speed boost.
+# Energy drain while boosted is a later ticket (#62).
+
+var capability_id := "distorder"