feat: 增强 Transfers 页面文件浏览功能

- 在 SftpFilePickerModal 中添加搜索功能
- 添加显示/隐藏文件切换按钮（参考 SftpView）
- Remote->Many 模式下目标连接列表自动排除源连接
- 全选功能自动排除源连接
- 添加空状态提示信息
- 优化用户体验和交互逻辑

docs/design-system/MASTER.md

@@ -0,0 +1,43 @@
+# SSH Manager Transfer Console - Design System (Master)
+
+Goal: a fast, reliable, ops-style UI for moving data across many hosts.
+
+Design principles
+- Transfer-first: primary surface is "plans / queue / progress"; connections are supporting data.
+- Dense but calm: show more information without visual noise; consistent rhythm and spacing.
+- Failure is actionable: errors are specific, local to the job, and keep context.
+- Keyboard-friendly: visible focus rings, logical tab order, no hover-only actions.
+
+Color and surfaces (dark-first)
+- Background: deep slate with subtle gradient + faint grid/noise.
+- Surfaces: layered cards (solid + slight transparency) with visible borders.
+- Accent: cyan for primary actions and progress.
+- Status:
+  - Success: green
+  - Warning: amber
+  - Danger: red
+
+Typography
+- Headings: IBM Plex Sans (600-700)
+- Body: IBM Plex Sans (400-500)
+- Mono (paths, hostnames, commands): IBM Plex Mono
+
+Spacing and layout
+- App shell: left rail (nav) + main content; content uses max width on desktop.
+- Cards: 12-16px padding on mobile, 16-20px on desktop.
+- Touch targets: >= 44px for buttons / list rows.
+
+Interaction
+- Buttons: disable during async; show inline spinner + label change ("Starting…").
+- Loading: skeleton for lists; avoid layout jump.
+- Motion: 150-250ms transitions; respect prefers-reduced-motion.
+
+Accessibility
+- Contrast: normal text >= 4.5:1.
+- Focus: always visible focus ring on interactive elements.
+- Icon-only buttons must have aria-label.
+
+Transfer UX patterns
+- "Plan" = input + targets + options; "Run" produces jobs in a queue.
+- Queue rows show: source, targets count, status, progress, started/finished, retry.
+- Progress: per-target progress when available (XHR upload), otherwise discrete states.