* feat(mobile): split controls into separate Agent and Model buttons
- Add MobileAgentButton with tap-to-cycle and long-press-to-open behavior
- Add MobileModelButton for direct model panel access
- Remove agent selection from UnifiedControlsDrawer for cleaner mobile UX
- Agent cycling accessible via Tab key shortcut
* fix(mobile): optimize controls layout and touch handling
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Co-authored-by: Jovines <jovines@qq.com>
