#### Background
The Android and iOS mobile apps have had the saved tab and custom reading lists for many years now. They have had slightly different functions on Android versus iOS, but custom lists have always been shared and synced on the server. This year, the Web team is adding a "Saved" function, and they will support saving articles to one list, and soon after custom lists. We want to make sure that the experience matches across Web and the mobile apps when users simply saves something, and adds it to a custom list.
#### User story
As a Wikipedia reader who uses the Saved tab, I want an "All Articles" view that shows everything I've saved across all my collections in one place, so that I never have to browse individual collections to find a specific article.
#### Requirements
"All articles" view
- Add "All articles" option within Saved,
- "All articles" displays every article saved across all lists, including in the default list, and custom lists
- Articles appear only once, even if they belong to multiple lists
- Custom lists remain unchanged and continue to function as before
- When viewing "All articles", each article should show which custom lists it's on within Saved (match current behavior when searching for an article within teh "Filter" funtionality)
Unsave behavior from Saved tab
- Unsaving from "All Articles" removes the article from ALL lists it belongs to: it is fully removed from the user's saved content: Show a confirmation prompt before deletion (See iOS for precedent), Prompt must clearly communicate that the article will be removed from all lists, not just one
- Unsaving from a custom list only removes the article from that list; the article remains in "All Articles"
Nice to have: Update filter to search
- Change "Filter" functionality to a Search icon
- Search whichever view is active: if All articles are active, search article titles. If Collections view (reading lists) is active, search through reading list titles (matching iOS functionality)
#### Design
https://www.figma.com/design/Xuxn2U14hNcxmDdi3TpIhO/Reading-lists?node-id=311-4400&p=f&t=LEbqJfLKotMg9OD4-0