## Summary
Refactors `BaseModalLayout` from a flexbox-based layout to CSS Grid,
enabling smoother panel transitions and improved layout control.
## Changes
### Layout Restructure
- **Flexbox → CSS Grid**: Replaced nested flexbox with a 3-column CSS
Grid (`nav | main | aside`)
- **Smooth panel transitions**: Panel show/hide now animates via
`grid-template-columns` instead of Vue `<Transition>` with `translateX`
- **Removed transition CSS**: Deleted `.slide-panel-*` and `.fade-*`
transition styles (no longer needed with grid approach)
### Right Panel Improvements
- **Dedicated header**: Added header with close button, right panel
toggle, and customizable title slot (`rightPanelHeaderTitle`,
`rightPanelHeaderActions`)
- **New prop**: Added `rightPanelTitle` prop for simple text title in
right panel header
### UX & Accessibility
- **ESC key handling**: Pressing Escape closes the right panel (if open)
before closing the dialog
- **Accessibility**: Added `aria-label` attributes to all panel toggle
and close buttons
- **i18n**: Added translation keys: `showLeftPanel`, `hideLeftPanel`,
`showRightPanel`, `hideRightPanel`, `closeDialog`
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Co-authored-by: Amp <amp@ampcode.com>
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