Expose worktree import (openExternalWorktree/importAllWorktrees) via CLI and MCP #6051

Summary

The desktop app can import an already-existing git worktree into a workspace (Project Settings → Import), backed by openExternalWorktree / importAllWorktrees in apps/desktop/src/lib/trpc/routers/workspaces/procedures/create.ts. Neither packages/cli nor packages/mcp expose this capability — workspaces create / the MCP create_workspace tool only ever create a new worktree; there's no way to hand Superset a worktree path that already exists on disk from the CLI or MCP surface.

Use case

Automation flows that need to pre-create a worktree/branch under their own naming rules (e.g. a Linear "Work on issue → Custom script" integration that derives branch names from a team's own git workflow conventions) before handing the workspace over to Superset for session/agent management. Today there's no scriptable way to do this without either:

• letting Superset create its own worktree (losing control over branch naming/pre-flight checks), or
• manually clicking Import in the desktop UI (breaks full automation).

Request

Expose the existing import capability on the automatable surfaces:

• CLI: superset workspaces import --project <id> --path <worktree-path> --branch <branch> (mirroring the existing openExternalWorktree mutation's inputs: projectId, worktreePath, branch)
• MCP: a matching import_workspace (or similar) tool alongside create_workspace

Notes

workspaces create --branch <name> does reuse an orphaned worktree/workspace if one already exists for that exact branch that Superset itself tracks, but there's no way to point it at an arbitrary pre-existing worktree path it doesn't already know about.