feat: Add /kb-add command for quick video addition

- Add cmd_add() function to support adding single videos to inbox
- Support BV IDs, full URLs, and short links (with friendly warning)
- Add --process flag to immediately process after adding
- Add --yes flag to skip confirmation prompts
- Update SKILL.md with /kb-add command documentation

skills/obsidian-kb/SKILL.md

@@ -11,6 +11,7 @@
 
 | 命令 | 描述 | 用法 |
 |------|------|------|
+| `/kb-add` | 添加单个视频 | `/kb-add <URL> [--process] [--yes]` |
 | `/kb-subscribe` | 订阅内容源 | `/kb-subscribe <source>:<type>:<id>` |
 | `/kb-inbox` | 查看收件箱 | `/kb-inbox [--limit N]` |
 | `/kb-process` | 处理内容 | `/kb-process [content_id]` |
@@ -20,6 +21,43 @@
 
 ## 命令详解
 
+### /kb-add
+
+快速添加单个视频到收件箱。
+
+**用法:**
+```
+/kb-add BV1xx411c7mD
+/kb-add "https://www.bilibili.com/video/BV1xx411c7mD"
+/kb-add "https://www.bilibili.com/video/BV1xx411c7mD" --process
+/kb-add BV1xx411c7mD --yes
+```
+
+**参数:**
+- `<URL>` - 视频URL或BV号
+  - 完整URL: `https://www.bilibili.com/video/BVxxxxx`
+  - BV号: `BVxxxxx`
+  - 短链接: `https://b23.tv/xxxxx`（显示友好提示）
+- `--process` - 添加后立即处理
+- `--yes` - 跳过确认提示
+
+**输出示例:**
+```
+📥 正在添加视频: BV1xx411c7mD
+  → 标题: Python编程入门教程
+  → UP主: CodeMaster
+  → 时长: 3600秒
+  → 获取字幕... ✅
+
+✅ 视频已添加到收件箱!
+   Content ID: abc123def456
+
+💡 使用以下命令处理:
+   python3 src/cli.py process abc123def456
+   或:
+   python3 src/cli.py process all
+```
+
 ### /kb-subscribe
 
 订阅一个内容源，支持自动获取更新。