feat: adopt material 3 theme and billing adjustments

lib/widgets/common/buttons/primary_button.dart

@@ -1,5 +1,4 @@
 import 'package:flutter/material.dart';
-import '../../../theme/app_colors.dart';
 
 /// 주요 액션에 사용되는 Primary 버튼
 /// 저장, 추가, 확인 등의 주요 액션에 사용됩니다.
@@ -44,26 +43,30 @@ class _PrimaryButtonState extends State<PrimaryButton> {
   Widget build(BuildContext context) {
     final theme = Theme.of(context);
     final effectiveBackgroundColor =
-        widget.backgroundColor ?? theme.primaryColor;
+        widget.backgroundColor ?? theme.colorScheme.primary;
     final effectiveForegroundColor =
-        widget.foregroundColor ?? AppColors.pureWhite;
+        widget.foregroundColor ?? theme.colorScheme.onPrimary;
 
     Widget button = AnimatedContainer(
       duration: const Duration(milliseconds: 200),
       width: widget.width ?? double.infinity,
       height: widget.height,
       transform: widget.enableHoverEffect && _isHovered
-          ? (Matrix4.identity()..scale(1.02))
+          ? Matrix4.diagonal3Values(1.02, 1.02, 1.0)
           : Matrix4.identity(),
       child: ElevatedButton(
         onPressed: widget.isLoading ? null : widget.onPressed,
         style: ElevatedButton.styleFrom(
           backgroundColor: effectiveBackgroundColor,
           foregroundColor: effectiveForegroundColor,
+          // 고정 높이와 텍스트 잘림 방지를 위해 최소 사이즈 지정
+          minimumSize: Size.fromHeight(widget.height),
           shape: RoundedRectangleBorder(
             borderRadius: BorderRadius.circular(widget.borderRadius),
           ),
-          padding: widget.padding ?? const EdgeInsets.symmetric(vertical: 16),
+          // 컨테이너에서 높이를 관리하므로 수직 패딩은 0으로 두고
+          // 수평 여백만 부여하여 작은 높이(예: 48)에서 글자 잘림 방지
+          padding: widget.padding ?? const EdgeInsets.symmetric(horizontal: 16),
           elevation: widget.enableHoverEffect && _isHovered ? 2 : 0,
           shadowColor: Colors.black.withValues(alpha: 0.08),
           disabledBackgroundColor: