Add dashboard swap/remove toggles and removal confirmation

[multiplex55]

Motivation

• Provide UI switches to hide swap and remove controls in the dashboard editor to reduce clutter when not needed.
• Make slot removal safer by requiring an explicit confirmation before a slot is deleted.
• Ensure the "Show swap" toggle hides both per-slot swap controls (the Swap button and the Swap with selected button).

Description

• Added boolean fields show_swap_buttons and show_remove_buttons and a confirm_remove_slot: Option<usize> to DashboardEditorDialog with sensible defaults in Default::default.
• Added two checkboxes to the top control row: Show swap (bound to show_swap_buttons) and Show remove (bound to show_remove_buttons).
• Wrapped per-slot header actions so the Remove button is only shown when show_remove_buttons is true and both the Swap and Swap with selected controls are only shown when show_swap_buttons is true.
• Implemented a non-blocking confirmation dialog using an egui::Window that displays Remove slot '{label}'? (using Self::slot_label(...)) and only marks a slot for removal when the user confirms; actual removal is gated by the confirmation state (confirm_remove_slot / confirm_remove).

Testing

• No automated tests were executed for this change.

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Codex Task