Project labels: option to use the folder name for grouped projects

[SpyC0der77]

Problem

When two checkouts of the same repository are grouped into one logical project, T3 names the group by its GitHub identity (owner/repo) whenever the checkout titles differ. That label is used in the new-thread hero, the project picker, and the sidebar.

For people who keep multiple clones or worktrees of one repository, the folder name is the useful identifier. Right now the new-thread screen shows both identities but never reconciles them:

• Breadcrumb: arc-skeleton-for-zen / New thread
• Hero: What should we build in SpyC0der77/arc-ui-skeleton?

The hero names a project I did not select, and the selected folder only appears in the small breadcrumb.

This is also a consistency bug

Even setting the naming preference aside, the screenshot shows one screen naming the same target two different ways: the breadcrumb says arc-skeleton-for-zen, while the hero says SpyC0der77/arc-ui-skeleton. The selected project is the folder, so the primary heading should not replace it with a different project identity without reconciling the two.

If owner/repo remains the intended label for grouped projects, the hero should at least show the selected checkout as secondary context. The Folder option above would make both surfaces agree by construction.

Tracked separately as #24999.

Proposal

Add a Project labels preference next to Project grouping in Settings → General → Organization:

• Repository (owner/repo) — current behavior.
• Folder (the checkout's project title, e.g. arc-skeleton-for-zen).

In Folder mode, use the selected or representative checkout's title for the sidebar project row, project picker, and new-thread hero. For a group containing multiple checkouts, show the repository as secondary context (subtitle, badge, or tooltip) so the group is still identifiable.

Default to Repository so this is opt-in and the mobile naming from #17611 stays unchanged.

Why not just turn off Project grouping?

That works today, but it is global: it also ungroups repositories across machines and removes the grouping benefit for people who deliberately keep several checkouts. The per-project Group into... → Keep separate override is only exposed in the legacy sidebar, so current-sidebar users have to choose between grouping and recognizable names.

Workaround today

Settings → General → Organization → turn off Project grouping, or enable the legacy sidebar and use Group into... → Keep separate for the checkout.

[SpyC0der77]

Tracking the consistency bug separately as #24999. This thread stays focused on the Repository/Folder label setting.