feat(app): 创建贴纸选择底部面板 — 6 类 60 个 emoji 贴纸

app/lib/features/editor/widgets/sticker_picker_sheet.dart

@@ -0,0 +1,97 @@
+// 贴纸选择底部面板
+//
+// Phase 1 使用内置 emoji 贴纸（6 类 60 个），后续替换为贴纸包资源。
+// 分类：心情/动物/自然/食物/学校/装饰
+
+import 'package:flutter/material.dart';
+
+/// 贴纸选择底部面板
+class StickerPickerSheet extends StatelessWidget {
+  final void Function(String emoji) onStickerSelected;
+
+  const StickerPickerSheet({
+    super.key,
+    required this.onStickerSelected,
+  });
+
+  // Phase 1 内置贴纸集
+  static const _stickerCategories = <String, List<String>>{
+    '心情': ['😊', '😢', '😡', '🤔', '😐', '🥰', '😋', '🤗', '😴', '🎉'],
+    '动物': ['🐱', '🐶', '🐰', '🐻', '🦊', '🐼', '🐨', '🦄', '🐸', '🦋'],
+    '自然': ['🌸', '🌺', '🌻', '🍀', '🌈', '⭐', '🌙', '☀️', '❄️', '🍃'],
+    '食物': ['🍰', '🍩', '🍦', '🍓', '🍎', '🧁', '🍪', '🍕', '🍔', '🥤'],
+    '学校': ['📚', '✏️', '🎨', '📝', '📐', '🎒', '🏆', '📖', '💡', '🔔'],
+    '装饰': ['💕', '✨', '🎀', '🎵', '🎶', '💫', '🦋', '🌸', '🍀', '💎'],
+  };
+
+  @override
+  Widget build(BuildContext context) {
+    return Container(
+      height: 320,
+      decoration: BoxDecoration(
+        color: Theme.of(context).colorScheme.surface,
+        borderRadius: const BorderRadius.vertical(top: Radius.circular(22)),
+      ),
+      child: Column(
+        children: [
+          // 拖拽条
+          Center(
+            child: Container(
+              margin: const EdgeInsets.symmetric(vertical: 8),
+              width: 40,
+              height: 4,
+              decoration: BoxDecoration(
+                color: Colors.grey.shade300,
+                borderRadius: BorderRadius.circular(2),
+              ),
+            ),
+          ),
+          // 分类标签
+          SizedBox(
+            height: 40,
+            child: ListView(
+              scrollDirection: Axis.horizontal,
+              padding: const EdgeInsets.symmetric(horizontal: 16),
+              children: _stickerCategories.keys.map((category) {
+                return Padding(
+                  padding: const EdgeInsets.only(right: 8),
+                  child: Chip(
+                    label: Text(category, style: const TextStyle(fontSize: 13)),
+                    visualDensity: VisualDensity.compact,
+                  ),
+                );
+              }).toList(),
+            ),
+          ),
+          const Divider(height: 1),
+          // 贴纸网格
+          Expanded(
+            child: GridView.count(
+              crossAxisCount: 5,
+              padding: const EdgeInsets.all(16),
+              mainAxisSpacing: 8,
+              crossAxisSpacing: 8,
+              children: _stickerCategories.values
+                  .expand((list) => list)
+                  .map((emoji) {
+                return InkWell(
+                  onTap: () {
+                    onStickerSelected(emoji);
+                    Navigator.pop(context);
+                  },
+                  borderRadius: BorderRadius.circular(8),
+                  child: Center(
+                    child: Text(
+                      emoji,
+                      style: const TextStyle(fontSize: 32),
+                    ),
+                  ),
+                );
+              }).toList(),
+            ),
+          ),
+        ],
+      ),
+    );
+  }
+}