feat(player): add option to dock lyrics & queue as a side drawer

[WGlegola]

Summary

Adds a General → Behavior setting, "Open lyrics & queue as a side drawer", that docks the lyrics and queue panels as a right-hand column which pushes the content aside — like the left sidebar — instead of floating over it as a glass overlay.

The setting is off by default, so the existing floating behavior is unchanged for anyone who doesn't opt in.

Motivation

The lyrics/queue panels currently appear as a floating glass "popup" on the trailing edge. Some users prefer a docked drawer (matching the left sidebar) that reserves its own space and lets the main content reflow beside it, rather than overlaying it.

What changed

• SettingsManager — new persisted lyricsQueueDrawerEnabled flag (default false).
• GeneralSettingsView — the toggle in the Behavior section.
• MainWindow — mainContent is a single stable HStack so the NavigationSplitView keeps its identity when the setting toggles (a naive branch swap rebuilt it and reset scroll). Floating mode keeps the trailing overlay; drawer mode docks rightDrawerColumn as a sibling column. The drawer's material extends up behind the transparent titlebar so it reads full-height like the sidebar, while its content stays within the safe area so the Up Next Clear/Edit controls remain out of the window-drag strip and stay clickable. The AI/command-bar button remains a standard toolbar item.
• LyricsView / QueueView / QueueSidePanelView / SimpleLyricsView — a docked flag renders flush content (no fixed-width glass/material card); the drawer container supplies the background. The queue uses regular material rather than glass so NSTableView drag-and-drop keeps working.
• QueueSidePanelView — the docked side-panel table column is sized deterministically (container width minus a scroller gutter) so rows don't clip on the right edge in the narrower drawer.
• MainWindowLayout — rightDrawerWidth constant.

Behavior

Setting	Lyrics / Queue
Off (default)	Floating glass panel over the trailing edge (unchanged)
On	Docked right-hand drawer that pushes content aside

Toggle it under Settings → General → Behavior.

Screenshots

Testing

• swift build, swiftlint --strict, and swiftformat clean.
• swift test --skip KasetUITests — full suite passes (2285 tests).
• Verified manually: toggle on/off, docked lyrics + queue (list and side-panel/Edit modes), drag-and-drop reorder in the docked panel, Clear/Edit clickability, and the side-panel rows no longer clipping.

Notes

• No third-party dependencies.
• Default off; no behavior change unless the user opts in.