Add wiki pages to recently viewed items
## Stakeholders
* Frontend (25% of total change): @vanessaotto
* Backend (75% of total change): @rchanyj
## What does this issue do and why?
Add wiki pages to recently viewed items. @afracazo noticed they are not present in recently viewed items and stated the following:
> One gap I've noticed: wiki pages don't appear in the **Recently viewed** section at all. As someone on the Knowledge team working on wiki functionality daily, I visit wiki pages frequently across different projects and groups, but none of that activity is reflected in Quick Access.
>
> The challenge with wikis is discoverability, they live at both group and project levels, and remembering which wiki has the information you need is a real friction point. Surfacing recently viewed wiki pages in Quick Access would directly address this.
## Design considerations
Based on feedback from the personalized homepage rollout, ensure that:
- Wiki page icons are clear and intuitive (avoid confusion with work item terminology)
- Wiki pages integrate seamlessly with existing recently viewed issues and merge requests
## Implementation Details
From @vanessaotto [here](https://gitlab.com/gitlab-org/gitlab/-/work_items/553938#note_3141510865):
> Looks like we need to create two separate 'real' MRs. Roughly 3/4 of the changes of the Spike MR would be ~backend related, and the 1/4 ~frontend. We need to split them to prevent **multiversion compatibility** between adding new fields via GraphQL and requesting this data in the browser.
>
> I can prepare the ~frontend in a MR so we can test the full flow together, but merge independently. @mmacfarlane would you like one of our team members to work on the ~backend code?
>
> P.S. with multiversion compatibility I'm not sure if we actually have to wait a full milestone between the releases. But we can discuss it within an issue or within the MRs.
## Related MR(s)
[!226353 (closed)](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/226353)
---
## Progress Summary
### :white_check_mark: What has been released
| Feature | Details |
|---------|---------|
| **Project wiki support** | Project-level wiki pages appear in recently viewed items and search autocomplete. Viewer permissions are enforced: pages the user no longer has access to are not shown. |
| **Group wiki support** | Group-level wiki pages (Premium/Ultimate) are surfaced in recently viewed items and search autocomplete. |
| **Deleted wiki pages filtered out** | Deleted wiki pages no longer appear in recently viewed items or search autocomplete, consistent with the behaviour of other item types (e.g. issues). |
**\[Docs\] MRs updating documentation with feature flag and feature release information:**
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/237395
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/237796
### :warning: Known quirks to address (future iterations)
| Issue | Summary |
|-------|---------|
| [#596576](https://gitlab.com/gitlab-org/gitlab/-/work_items/596576) | **Title update not reflected in recently viewed; updated title not picked up by search.** After updating a page title, recently viewed continues to show the old path. If the new title differs significantly from the original, the page becomes undiscoverable via search. |
| [#596577](https://gitlab.com/gitlab-org/gitlab/-/work_items/596577) | **Updating page path creates a stale duplicate entry; deleted page entry persists and leads to "page doesn't exist".** Updating a path leaves the old entry in recently viewed. If the page is then deleted, the stale old-path entry remains and navigates to an error page. |
| [#596578](https://gitlab.com/gitlab-org/gitlab/-/work_items/596578) | **Recreating a deleted page with the same path causes it to not appear in recently viewed or search autocomplete.** The `deleted_at` marker on the page meta record is never cleared on recreation, so the page remains invisible to recently viewed and search. |
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