feat(C-02)：工具热榜周榜+最近使用

新增ToolUsageRecord使用日志（tool+created_at索引）；/tool/top/总榜按累计排序、周榜按近7天聚合（无日志回退总榜，兼容period旧参）；/tool/recent/登录去重倒序；seed新增AI图片放大/代码运行两个工具。

tool/models.py

@@ -127,6 +127,45 @@ class ToolFavorite(models.Model):
         return f'{self.user} favorites {self.tool}'
 
 
+class ToolUsageRecord(models.Model):
+    """工具使用日志：用于周榜等时间窗聚合统计"""
+    tool = models.ForeignKey(
+        Tool,
+        on_delete=models.CASCADE,
+        related_name='usage_records',
+        verbose_name='工具'
+    )
+    user = models.ForeignKey(
+        settings.AUTH_USER_MODEL,
+        on_delete=models.SET_NULL,
+        null=True,
+        blank=True,
+        related_name='tool_usage_records',
+        verbose_name='用户'
+    )
+    session_id = models.CharField(
+        max_length=64,
+        blank=True,
+        default='',
+        verbose_name='会话ID'
+    )
+    created_at = models.DateTimeField(
+        auto_now_add=True,
+        verbose_name='使用时间'
+    )
+
+    class Meta:
+        verbose_name = '工具使用记录'
+        verbose_name_plural = '工具使用记录'
+        ordering = ['-created_at']
+        indexes = [
+            models.Index(fields=['tool', 'created_at']),
+        ]
+
+    def __str__(self):
+        return f'{self.tool} used at {self.created_at}'
+
+
 class CompressionHistory(models.Model):
     COMPRESSION_MODE_CHOICES = [
         ('lossy', '有损压缩'),