docs: project Bookmarks tab, home page section, and bookmark permissions

[nishantmonu51]

• Documents the project Bookmarks tab (feat: project-wide bookmark manager with a -/bookmarks tab and home page section #9863): the personal and managed categories, search, sort, and the edit and delete actions. Home bookmarks aren't listed there since fix: skip home bookmarks in the bookmark listings #9952; the page points to the dashboard's home button instead.
• Adds the Bookmarks section on the project home page and a permissions table covering personal, managed, and home bookmarks.
• Notes that managed bookmarks are listed for everyone with access to the project, even for dashboards blocked by security policies, so their names and descriptions shouldn't contain sensitive information.
• Adds three screenshots under docs/static/img/explore/bookmarks/.

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!