Add reusable UI components for Phase 7 UI Polish

- Introduced `EmojiQuickGrid`, `FontPresetPicker`, and `PresetSizeToggle` classes for emoji selection, font presets, and size toggles respectively.
- Implemented configuration methods for each component to handle dynamic content and theming.
- Created tests for the new components to ensure functionality and integration with the existing UI.
- Added a comprehensive architecture specification for Phase 7 UI Polish detailing scope, implementation, and validation strategies.
- Updated existing theme handling to support new UI elements and ensure consistent styling across the application.

scripts/thumbnails/thumbnail_cache.gd

@@ -4,6 +4,27 @@ extends RefCounted
 const STICKMEN_DIR := "user://thumbnails/stickmen"
 const PROP_DIR := "user://thumbnails/props"
 const PROP_VERSION := 1
+var _memory: Dictionary = {}
+
+func get_texture(cache_path: String) -> Texture2D:
+	if _memory.has(cache_path):
+		return _memory[cache_path] as Texture2D
+	var texture: Texture2D = load_png(cache_path)
+	if texture != null:
+		_memory[cache_path] = texture
+	return texture
+
+func store_texture(cache_path: String, texture: Texture2D) -> Error:
+	if texture == null:
+		return ERR_INVALID_PARAMETER
+	_memory[cache_path] = texture
+	return save_png(texture, cache_path)
+
+func forget_memory(cache_path: String) -> void:
+	_memory.erase(cache_path)
+
+func clear_memory() -> void:
+	_memory.clear()
 
 
 func stickman_key(path: String) -> String:
@@ -19,12 +40,16 @@ func prop_png(id: String) -> String:
 
 
 func load_png(png_path: String) -> Texture2D:
+	if _memory.has(png_path):
+		return _memory[png_path] as Texture2D
 	if not FileAccess.file_exists(png_path):
 		return null
 	var img := Image.load_from_file(png_path)
 	if img == null:
 		return null
-	return ImageTexture.create_from_image(img)
+	var texture: Texture2D = ImageTexture.create_from_image(img)
+	_memory[png_path] = texture
+	return texture
 
 
 func save_png(tex: Texture2D, png_path: String) -> Error:
@@ -34,6 +59,7 @@ func save_png(tex: Texture2D, png_path: String) -> Error:
 	if img == null:
 		return ERR_CANT_CREATE
 	ensure_dir(png_path.get_base_dir())
+	_memory[png_path] = tex
 	return img.save_png(png_path)