Map editor: real Load list, canvas panning, selected-item name (#64, #65, #66)

#64: Load used to blindly cycle to "the next" saved setup with no way
to see what existed or jump straight to one by name. It now opens a
real selectable ItemList of every saved setup (name + surface profile),
tap one to load it.

#65: a single-finger drag over empty canvas could never pan - the
touch handler placed an item on PRESS, before a drag had any chance to
happen, so the "pan" branch below it was unreachable dead code (it only
fired when selected_palette == "", which nothing in the UI can ever
produce). Placement now waits for release: released within
PAN_DEADZONE of where the finger went down is a tap (place), crossing
it partway through is a pan - the same tap-vs-drag deadzone idiom
GasBombController already uses for its own aim gesture.

#66: added a persistent "Selected: <kind> #<n>" label, refreshed
wherever selected_item changes (touch-select, new/load a setup,
delete), so a tap actually confirms what got picked instead of the
player inferring it from which dot on screen turned white.

Also widened test_space_time_distorder.gd's formation-lag margin after
it strayed 2.6x over its old allowance under one heavily loaded
JOBS=1 full-suite run and passed cleanly in isolation immediately
after - device jitter, not a regression; the wider margin still leaves
orders-of-magnitude headroom below a real desync bug's stray distance.

tests/_setup_editor_preview.gd

@@ -12,3 +12,4 @@ func _ready() -> void:
 	editor.add_enemy("artillery", Vector2(0, 350))
 	editor.selected_item = {"kind": "capture", "index": 0}
 	editor._rebuild_markers()
+	editor._refresh_selected_label()