fix(theme): drop redundant const preloads shadowing global class_names

palette.gd / theme_keys.gd already declare `class_name`, so `const Palette =
preload(...)` in every consumer shadowed the global class and emitted 4
editor errors ("has the same name as a global class"). Reference the global
class_names directly. Editor reload now clean; suite 125/125; runtime probe
still builds all 75 showcase nodes with the theme applied.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

client/scripts/theme/surfaces/dark_bay.gd

@@ -4,7 +4,6 @@ extends Panel
 ## Uniforms are set at runtime from Palette (deliberate deviation from spec §5.4's
 ## "baked into the .tscn/material" approach) — keeps Palette the single source of
 ## truth at the cost of an editor preview; the surface renders once the scene runs.
-const Palette = preload("res://scripts/theme/palette.gd")
 
 
 func _ready() -> void: