Workspaces

Add workspace commands, log view improvements, and bump version to 0.4.8

New commands: "JJ: Workspace List" (select to view a workspace working-copy
diff), "JJ: Workspace Add..." (creates the workspace and opens it in a new
window), "JJ: Workspace Forget..." (multi-select), "JJ: Workspace Rename",
and "JJ: Workspace Update Stale".

jj does not record workspace directory paths, so the list command cannot
open existing workspace folders; only newly created workspaces are opened
automatically.

Log view reordering: alt+up and alt+down swap the change under the cursor
with its child or parent for linear stack reordering, implemented as
jj rebase --insert-after / --insert-before. Changes with multiple parents
or children are refused.

Log view chrome: hovering an entry shows a detail card with the full
description, author, timestamps, a diff stat, and clickable edit, diff,
squash, and abandon actions; right-aligned region annotations show each
entry relative age, bookmarks, and working-copy or conflict markers; the
entry under the cursor is outlined; and the gutter marks the working copy
(circle) and conflicted entries (dot). The graph metadata query now
returns full per-change information and the log template gains a relative
age field.