Workspace menu: list every worktree, not only the previous one

[armanarutiunov]

Problem

When I start a new thread, the Workspace menu offers three choices:

• Current checkout
• New worktree
• Previous worktree (only the most recently used one)

I usually have several worktrees open for one repo. To start a thread in any of the others, I have to know that the branch picker switches the thread to a branch's worktree. Nothing in the Workspace menu says so. The two controls sit apart and look unrelated, so the Workspace menu reads as the complete list.

This was raised before. @Wiktor102 hit the same thing in #3796 (comment):

I didn't realize it switches the worktree when I switch branches until I read through #3798.

#3796 asked for an "Existing worktrees" group. It was closed as a duplicate of #1047. #1047 is done through the branch picker, so the Workspace menu never changed.

Proposal

Replace the single "Previous worktree" row with a short list of the project's worktrees:

• Show each worktree's branch name, plus its folder name if they differ.
• Sort by most recent use, so the current "Previous worktree" stays at the top.
• Cap the list (for example 5), with a "More…" row or a search field when there are more.
• Picking a row does what picking that branch in the branch picker does today.

The data already exists. The branch picker already knows which branches have a worktree (its worktree badge), so this is a UI change. It needs no new server work.

Questions for maintainers

1. Is this direction OK, or would you rather keep the menu small and make the branch picker easier to discover?
2. Should the list include worktrees created outside T3 Code (git worktree add, JetBrains), or only the ones T3 Code threads used? The branch picker already shows both.
3. Mobile has its own new-task flow. Should it get the same change in the same PR, or later?

I'm happy to open a PR with before/after captures once the scope is agreed.