#18127 next: workspace groups as categories above All

Summary

Your workspace groups now sit above the Projects header as top-level categories. While any group exists, the header over the loose rows reads "All". Without groups it still reads "Projects".

• SidebarLayoutOptions.groupsAsCategories: for the only machine's section, groups draw first, then the header, then the loose workspaces. Collapsing the header hides only the loose rows.
• Rows keep their model sibling indices, so drag-and-drop resolution (index-based) and keyboard order are unchanged. Keyboard order follows the drawn order.
• SidebarRow.titlesAll drives the "All" title. New string sidebar.section.all is in all 21 locales; non-English values are marked needs_review.

Stacked on #18120 and #18124 (the diff includes them until they land). This is PR 3 of the sidebar categories job.

Testing

• Failing test first: d9a3e7de056 (SidebarGroupsAsCategoriesTests). The fix is in f6fede1895e.
• Local: package conventions lint, god-file, concurrency, crash-safety and l10n checks all pass.
• Fleet build 4bd9ec5f656bbd09da7ef6eb of d186c530f93: a new group draws above the list, which is titled All.

Captures

Same seed on each build: three workspaces, one in a new group. Before is the #18124 build; after is this PR's fleet build. Light is Rose Pine Dawn, dark is Rose Pine.

	Before	After
Light
Dark

Changelog

Changed: Workspace groups appear above the project list as categories, and the list is titled "All" while groups exist.

🤖 Generated with Claude Code

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Summary by cubic

Workspace groups now render as top-level categories above the Projects header. When a group exists, the header reads “All” for loose workspaces; otherwise it remains “Projects,” while workspace indices stay unchanged for drag-and-drop.

• Projects can be hidden from the sidebar menu or Settings via sidebar.showProjects; Chats can be hidden from its header via sidebar.showChats.
• Hidden Projects can be restored with Show Hidden Sections, while Chats remains opt-in through Settings.
• Collapsed layout sections persist across relaunches in UserDefaults.
• Adds localized strings, action-surface exports, and tests for group ordering, visibility settings, menus, and persistence.

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[!NOTE]
Medium Risk
Touches sidebar layout, persisted view state, and cmux.json-backed visibility settings; mistakes could hide workspaces or break drag/keyboard ordering, but changes are localized to sidebar UX.

Overview
Workspace groups on the sole machine section now render above the built-in header as top-level categories; when any group exists that header labels the loose workspaces "All" instead of "Projects", while row indices stay model-based so drag-and-drop and keyboard order still match resolution logic.

Hide / show sidebar bands adds GUI actions to turn off Projects (sidebar.showProjects) or Chats/Recents (sidebar.showChats), restore Projects via Show Hidden Sections or Settings, and wire section-header context menus so only Recents gets Hide Section. Collapsed layout sections (e.g. Chats) persist per Mac in UserDefaults through SidebarCollapsedSections.

Supporting work includes a Show Projects settings toggle, layout skipping when Projects is hidden (hidesWorkspaces), and localized strings for the new actions and "All" header title.

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