Redesign study navigation and light theme

tests/shell_navigation_test.gd

@@ -0,0 +1,24 @@
+extends SceneTree
+
+const NavigationRoutes := preload("res://scripts/ui/navigation_routes.gd")
+
+var failures := 0
+
+
+func _initialize() -> void:
+	_assert(NavigationRoutes.key_for_screen("selection", "exam") == "home", "exam selection should activate Home")
+	_assert(NavigationRoutes.key_for_screen("selection", "step3") == "practice", "Step 3 modes should activate Practice")
+	_assert(NavigationRoutes.key_for_screen("setup") == "practice", "block setup should activate Practice")
+	_assert(NavigationRoutes.key_for_screen("simulation_results") == "exams", "simulation results should activate Exams")
+	_assert(NavigationRoutes.key_for_screen("ccs_review") == "ccs", "CCS review should activate CCS Cases")
+	_assert(NavigationRoutes.key_for_screen("profile") == "performance", "profile should activate Performance")
+	_assert(NavigationRoutes.key_for_screen("map") == "study_plan", "study map should activate Study Plan")
+	_assert(NavigationRoutes.key_for_screen("settings") == "settings", "settings should activate Settings")
+	quit(1 if failures > 0 else 0)
+
+
+func _assert(condition: bool, message: String) -> void:
+	if condition:
+		return
+	failures += 1
+	push_error(message)