feat(sidebar): workspace groups — manual cross-repo bundles

[dragonfire1119]

Summary

Adds Workspace Groups: manually-named, cross-repo bundles of worktrees in the
sidebar. Backend + frontend workspaces for the same feature can now live under
one collapsible header with a shared color stripe that follows them through any
groupBy mode (flat, none, repo, pr-status, group) and into the
workspace board.

Design summary

• Single membership per worktree (workspaceGroupId on WorktreeMeta).
• 8-color palette subset of the workspace-status palette (no conductor-*).
• New 'group' view in the groupBy picker.
• Group members cluster contiguously in every view; 'group' view adds the
  header + collapse + drag-and-drop + Ungrouped bucket.
• Group color stripe rendered on each member card across sidebar + board.
• Status auto-syncs across group members. Changing one member's
  workspaceStatus propagates to all members of its group so a feature bundle
  moves through the board as one unit.
• Ungroup dissolves the group; workspaces survive as ungrouped.

Acceptance criteria

• 1. Right-click → "Add to group → New group…" → name → Enter creates a group
• 2. Add a workspace from a different repo to that group
• 3. Colored stripe visible on grouped workspaces in flat, none, repo,
  pr-status, group views
• 4. "Ungroup" dissolves group, members survive
• 5. "Remove from group" on single member; group survives
• 6. Restart app → groups, names, colors, sortOrder, collapse restored
• 7. Drag workspace onto group header → joins group
• 8. Drag workspace onto "Ungrouped" → cleared
• 9. Drag-reorder group headers persists across restart
• 10. Pinned grouped workspace appears under PINNED with color stripe

Test plan

• Unit tests passing (workspace-groups helpers, action helpers, persistence,
  cluster fns, IPC updateMeta pass-through)
• pnpm typecheck clean
• Manual AC Linux support #1-10 walked
• Screenshots / recording attached below

Screenshots

Workspace list:

Workspace Board:

Context menu:

View options:

[chansantheman]

I was thinking of such a thing the other day +1

[nwparker]

Looking at this!
@chansantheman you should join the Discord -- will be easier to chat.

But since you're here, can you let me know what your use case is?
Curious too @dragonfire1119 but I'll also ask on Discord

[chansantheman]

I am on discord - happy to convo there, but to answer you question: more of a workflow thing.

branches, worktrees, all support well, but worktrees allows for the mental model of multiple ais tackling same subject of a task.

ex. i work on various items at a time. it would be nice to group

feat 1 (gemini task, codex task, claude task) away from
feat 2 (gemini task, codex task, claude task) that looks exactly the same.

//

bug 1 (gemini task, codex task, claude task) away from
bug 2 (gemini task, codex task, claude task) that looks exactly the same.

[nwparker]

@chansantheman @dragonfire1119
What do you guys feel about this? Very rough idea

Will let you select multiple repos here.
Woudl that solve your asks? If not LMK! Just trying to gather info right now

[nwparker]

If you want to try/see :
#2384

Must enable under experimental