- Remove layer from KeybindingOptions reference
- Replace when:'mounted' with global:boolean in RegisteredKeybinding
- Add useGlobalKeybindings section with usage example
- Fix passthrough description to reflect actual bubble behaviour
- Update priority order list across core-concepts and architecture doc

Previously, global bindings were checked after the path walk, but capture
mode returned early inside the loop — so globals were never reached when a
capture-mode component (e.g. TextInput) had focus.

Restructured dispatch into three passes:
  1. Named bindings (walk focused node → root)
  2. Global bindings — checked before capture fires
  3. Capture mode (onKeypress) — only if no global binding matched

The trap boundary still prevents globals from escaping — capture fires
immediately on hitting the trap, then returns.

useGlobalKeybindings and the global flag on BindingEntry were solving
a problem better handled by registering bindings at the right scope.
Unhandled keys bubble naturally to ancestor scopes, so a root-level
useKeybindings call serves as an app-wide shortcut handler without
any special API.

- Delete useGlobalKeybindings hook
- Remove registerGlobalKeybindings from FocusStore
- Remove global flag from BindingEntry and RegisteredKeybinding
- Simplify dispatch: single pass, named bindings walk up the path,
  pendingCapture deferred until end, trap uses break not return
- Simplify useKeybindingRegistry: available is just the branch path

- Remove useGlobalKeybindings section from input.mdx
- Remove global field from RegisteredKeybinding reference
- Update priority order in core-concepts to reflect simplified dispatch
- Update architecture doc dispatch algorithm to match current implementation