Saved cross-list views / custom filters

[sjcotto]

"My Work" (/home) buckets assigned tasks by due date. Add user-defined saved views that span lists.

Scope

• Build cross-list/space queries with filter + sort + group, saved per user (e.g. "Everything due this week", "All my urgent tasks").
• Surface them in the sidebar; reuse lib/view-state.ts / applyViewState.

Acceptance

• Save a filter across multiple lists and reopen it from the sidebar.