Context

Users who are creating how-tos for each other may not be in the same gallery (example case: one class section may be making how-tos for another, or one class may be making how-tos for next year's class). So, the current implementation that only shows the how-tos for the gallery that the project is in, if the project is in a gallery, does not address this use case well. This PR implements a new filter button and ordering for how-tos, available as follows:

If the project is in a gallery and the user is viewing the Guide via the project editor:

• Users will be shown Mode that lets them see all how-tos that they have access to or only the how-tos in that gallery and any that they have bookmarked
• The how-tos will be in the following order: (1) bookmarked how-tos from any gallery, (2) how-tos from the current gallery, (3) (if in "all" mode) how-tos from all other galleries

If the project is not in a gallery and the user is viewing the Guide via the project editor OR the user is viewing the Guide via /guide:

• Users will see all how-tos from all of the galleries they have access to
• The how-tos will be in the following order: (1) bookmarked how-tos, (2) all other how-tos

Bookmarked how-tos are displayed with a 🔖 symbol.

I wrote this PR with minimal debugging support from Claude Code for three small bugs (of which it could not fix the second).

Related issues

• Related Issue #
• Closes New ordering for user-created how-tos in the project view panel #1087

Verification

1. Create two galleries, gallery A and gallery B. Make one how-to in gallery A and two how-tos in gallery B, with distinct titles so it is easy to know which gallery each how-to is in. Bookmark one of the how-tos in gallery B.
2. Open /guide. Verify that all three how-tos are visible and the Mode button for filtering is not visible. Verify that the bookmarked how-to is shown with a 🔖 . Verify that the bookmarked how-to is first.
3. Create a project. Do not add it to a gallery yet. Open the project viewer and the Guide panel. Verify the same thing as in step 2.
4. Add the project to gallery A. Verify that the filtering Mode button is now visible.
5. Set the filtering button to "all," then verify the same thing as in step 2. Additionally, verify that the how-to from gallery A is shown second and the non-bookmarked how-to is shown third.
6. Set the filtering button to "gallery + bookmarks only," then verify that: (1) the how-to from gallery A is visible, (2) the bookmarked how-to from gallery B is visible, (3) the non-bookmarked how-to from gallery B is not visible.
7. Set the filtering button back to "all" then verify per step 5.
8. Remove the project from the gallery and refresh the page. Verify per step 3.

Checklist