Cue List View: per-pane visibility toggle persisted in URL hash

[Copilot]

The Cue List View was always split into two panes with no way to focus on just one. This adds a three-way toggle — Top only / Both / Bottom only — with the selection round-tripped through the URL hash so it survives page loads and can be shared via QR code.

Store

• Added CueListViewMode = "both" | "top" | "bottom" type and viewMode field to CueListViewState (default: "both")

Hash persistence

• parseHash now reads view=top|bottom|both alongside trackId / identifier
• updateHash writes view back; omitted entirely when "both" to keep default URLs clean

Layout

• Top pane, splitter, and bottom pane are conditionally rendered based on viewMode
• Single-pane mode uses flex-1 to fill available height instead of a fixed percentage
• Splitter drag logic unchanged and only mounted when viewMode === "both"

Toggle UI

• Three icon buttons (PanelTop / Rows2 / PanelBottom) embedded in the bottom-pane controls header
• When in top-only mode (bottom pane hidden), a thin bar at screen bottom keeps the toggle reachable