Desktop app: support keyboard shortcut to switch agents (e.g. build/plan), like TUI's Tab/Shift+Tab #41742

Feature hasn't been suggested before.

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Describe the enhancement you want to request

What do you want to change or add?
Add a configurable keyboard shortcut in the desktop app to quickly switch between agents (e.g. build ↔ plan ↔ other custom agents), mirroring what the TUI already supports.

Currently in the TUI, agent_cycle (default Tab) and agent_cycle_reverse (default Shift+Tab) let users cycle between agents instantly, and these are customizable via tui.json. However, in the desktop app:

There is no documented keyboard shortcut to switch agents at all — users must click the agent selector in the UI each time.
Desktop prompt shortcuts (Ctrl+A/E etc.) are built-in and not configurable (per the docs), so there's no tui.json equivalent to add an agent-switching keybind.
What are the benefits?
Consistent UX across clients: Users coming from the TUI (or CLI/web) expect the same muscle memory (Tab / Shift+Tab) in the desktop app. The inconsistency forces relearning per client.
Faster workflow: Switching between plan and build is a frequent operation (draft a plan → execute). A keybind removes mouse round-trips, which matters a lot in long sessions.
Accessibility: Keyboard-only operation is essential for users who prefer not to touch the mouse, and for automation/streaming setups.
Proposal
Add agent-cycle keybinds to the desktop app (e.g. Tab / Shift+Tab, or at minimum a documented shortcut).
Make them configurable, ideally via the same tui.json keybinds mechanism (agent_cycle / agent_cycle_reverse) so one config works across TUI and desktop, or add an equivalent desktop setting.
Thanks for considering! The TUI already sets a good precedent; this would just bring the desktop app in line.