Add a bottom-docked horizontal clipboard history #1416

Summary

Add an optional bottom-of-screen clipboard history layout that presents the existing history as a full-width horizontal card shelf, while preserving the current floating panel modes.

Requirements

• Persist a bottom clipboard window position.
• Dock to the cursor monitor's work area above the macOS Dock or Windows taskbar.
• Remember dock height separately from floating-panel geometry.
• Render the complete history through horizontal virtualization.
• Use Left/Right for card navigation and modifier+Left/Right for categories.
• Preserve search, groups, preview, paste/copy, pin, favorite, delete, and shortcuts.
• Apply layout changes immediately and keep zh-CN/en-US copy in sync.
• Preserve macOS NSPanel and Windows keyboard-hook behavior.

Acceptance criteria

• Bottom mode spans the display work-area width and can be resized from its top edge.
• Follow Cursor, Center, and Remember restore the existing vertical panel.
• Dock and panel sizes do not overwrite one another.
• Show/hide animation cannot leave the shelf off-screen or race a rapid reopen.
• Frontend lint/type-check/build and Rust format/Clippy/tests pass on CI.