Redesign the Actions editor as a live pie menu

[danielchalmers]

Redesigns the Actions settings tab around a single idea: the editor is the menu. Instead of a ListBox with Add/Remove/Up/Down buttons next to a form, the tab now shows a full-size live pie where you work on the real thing. Fixes #16, since the editor itself is now the always-current preview.

How it works

• Click a slice to edit it. The inspector on the right binds to the selected slice and highlights it on the pie with the system accent color. Edits to name and icon appear on the slice as you type.
• Drag a slice around the ring to reorder. Reuses the same drag-reorder machinery as the live menu.
• Click the dashed "+" ghost slice to add an action. With no actions at all, the ghost becomes a clickable full ring.
• Hidden actions stay visible but dimmed in the editor so they can still be selected and edited.
• Drop files, apps, folders, or links anywhere on the pie card to add them as actions, same as before.
• Full keyboard support: the pie is focusable; arrow keys move the selection around the ring, Ctrl+Arrow reorders the selected action, Enter or Insert adds one, and Delete removes it.
• Screen reader support: a custom automation peer exposes the editor as a list of selectable action items plus an invokable "Add an action" button, with selection events raised as the user moves.
• The inspector gains Test, Duplicate, and Remove buttons and an icon + name header. Type-specific fields are unchanged.

Implementation notes

• PieControl gets an IsEditMode dependency property that renders all slices (disabled ones dimmed), appends the ghost slice, suppresses digit hints and the hub close target, and turns clicks into selection via a new TwoWay-bindable SelectedSlice property. The live menu path is untouched.
• Drag reorder now wraps over the full layout slot ring (including the ghost slot) so a full lap lands home, and drops on the ghost wedge clamp to the last real slot.
• PieControl now detaches its CollectionChanged/PropertyChanged handlers on unload, so the short-lived settings window no longer stays reachable from the app-lifetime actions collection after closing.
• PieAction.Clone() backs the Duplicate button so future properties can't be silently dropped from copies.
• MoveUpCommand/MoveDownCommand and the write-only SelectedActionIndex are gone; tests updated and extended (144 passing).

Verification

Drove the real SettingsWindow in an automated harness using genuine mouse and keyboard input (SendInput): click-to-select, live rename, ghost-slice add, Duplicate/Remove buttons, drag reorder (including a full-lap drag and a drop on the ghost wedge), hidden-action dimming, adding the first action from an empty editor, arrow-key selection, Ctrl+Arrow reorder, Enter add, Delete remove, and the UI Automation peer (child enumeration, SelectionItem.Select, and Invoke on the add button). All 26 checks pass, plus the full unit test suite.

Screenshots