int_speed/shd_speed granted +max_speed/+acceleration per level to a
single vessel, which is redundant now that #59/#62 gave the whole
fleet a shared speed fader instead - a per-ship speed stat has nothing
left to meaningfully affect since #59's multiplier is applied at the
point of use in Ship.gd regardless of the ship's own base stats.
Deleted both upgrade resources and their vessel-definition references
outright rather than leaving them unused.
test_ship_lab.gd's per-vessel-type isolation check used int_speed as
an arbitrary interceptor-only upgrade to prove it doesn't leak into
transporter stats - swapped to int_range, which still exists. Its
upgrade-card-count assertion updated for 3 remaining interceptor
upgrades instead of 4.
The fleet hold was unbounded - GameState.fleet_inventory had no
total_capacity, so a lone ship could carry unlimited resources. Capacity
is now data-driven: only vessels declaring the "cargo" capability
contribute their cargo_capacity stat (interceptor: 20; shield vessel and
gas bomber: 0, unarmed transporters are never in the fleet at all).
Fleet.gd recomputes it in the one place composition can change
(spawn_ships/add_ship/store_ship/_on_ship_destroyed), which also covers
the space<->surface scene-swap restore since that goes through
spawn_ships().
Rock.gd and GasVentField.gd (the two "fly over it to collect" pickup
paths) now check what collect_cargo()/collect_gas_cargo() actually
accepted before consuming their source, instead of assuming an
unlimited hold. The HUD's FLEET HOLD caption shows the live total/cap.
Also fixes test_resource_transfer.gd, which pushed more ore through a
2-ship fleet than the new cap allows - it now spawns the largest fleet
every unlocked doctrine permits, since that test is about the transfer
UI rather than the cap itself (test_fleet_cargo_limit.gd owns that).
