Editor: edit chrome view shell

[jonocodes]

The full-screen edit chrome view scaffold — the container the editor lives in. Spec: #87. Design: #82.

Scope

• New edit chrome view reached via select_view (reuses the MPRIS: mediabrowser widget schema, mpris.yaml layout, view-resolution hook #50 view-pinning protocol to suspend focus-driven auto-switching while editing; clear_view exits).
• Three-pane layout: palette · live-grid canvas · properties panel (Variant A). This ticket delivers the empty shell + pinning/exit lifecycle + a secondary layout picker (list of loaded layouts, switch without changing host focus, per New-layout creation flow #88).
• Save wiring to PUT /layouts/{id} (exists); create wiring lands with the creation-flow ticket.

Done when

• The edit view opens pinned to the focused app's resolved layout, the picker can switch layouts, and exiting reverts via clear_view. Panes are placeholders filled by the feature tickets.