feat: implement global saved views

Implements Phase 5 of SPEC 0030:
- Adds globalViews to global settings and global settings tab UI.
- Merges global saved views into board-local saved views list with a 'Global' badge.
- Displays query-only global saved views in the search bar filter editor.
- Prevents deletion of global saved views from board views.

Assisted-by: Antigravity <antigravity@google.com>