Add saved smart views across pages and collections

## Goal

[Add named collection views #101](https://github.com/Automattic/cortext/issues/101) organizes one collection at a time. It cannot answer questions that cross collection boundaries, such as "everything in Research changed this week."

Add saved queries that stay up to date across the whole workspace. A smart view can live on Home or inside another document.

## Tasks

- [ ] Add a query builder for collection traits, unassigned documents, dates, hierarchy, and compatible property values.
- [ ] Let users save, name, edit, duplicate, and delete a smart view.
- [ ] Render a consistent result list with each document's title, icon, assigned collections, and enough context to understand why it matched.
- [ ] Let a smart view be placed on Home or embedded inside a Cortext page.
- [ ] Refresh the results when matching documents or properties change. A smart view must never copy the documents it finds.

## Acceptance criteria

- A saved view can return unassigned documents and documents from more than one collection.
- Changing a matching collection trait, date, hierarchy position, or property updates the results.
- The same smart view can be opened from Home or embedded in a page.
- Opening a result uses the document's normal workspace route.
- Creating a smart view does not modify or duplicate the documents it finds.

Start by reading the existing named collection views described in #101, then trace how Home, documents, collections, and embedded Cortext pages currently render and navigate. Map the query builder, saved-view lifecycle, result rendering, and refresh behavior before implementing. Done means views work across collections, remain live without copying documents, and open results through normal workspace routes.

Written by the indexing model from the issue text.