[FEATURE] FleetView 'pin to top' shortcut (ctrl+t) isn't exposed in the keybindings config system

Feature request

Let the "pin to top" shortcut in FleetView's session list be rebound through ~/.claude/keybindings.json, the same way other shortcuts are.

Current behavior

In FleetView (the multi-session/agent dashboard), each session row shows a hint for pinning it to the top of the list: ctrl+t to pin to top / ctrl+t to unpin. This shortcut is hardcoded in the FleetView row UI rather than routed through the keybindings action registry documented at https://code.claude.com/docs/en/keybindings.

Consequences:

• ctrl+t can't be remapped for this action (e.g. to ctrl+p) via keybindings.json.
• It collides with the existing global default ctrl+t → app:toggleTodos, since FleetView appears to special-case the key locally rather than going through the shared binding resolution.
• FleetView/its row list isn't one of the documented rebindable contexts (Global, Chat, Footer, Tabs, etc.), so there's no way to discover or override this via the documented keybindings system at all.

Requested change

• Add a proper action id (e.g. fleetView:pinToTop / fleetView:togglePin) for this shortcut, bound to ctrl+t by default for backward compatibility.
• Expose the FleetView row list as a documented keybinding context so the action can be rebound like any other (e.g. to ctrl+p).

Why

Wanted to rebind pin-to-top from ctrl+t to ctrl+p for muscle-memory reasons and found there's no supported way to do it — the shortcut is invisible to the keybindings config system entirely.