feat(lanes): move the lane's git section into the Changes panel

- The branch line, the uncommitted-files hover panel and the git action
  row (fetch/pull/push/branch) move from the lane card to the top of the
  Changes panel (new LaneGitHeader.tsx); the card has no git row now.
- Header and panel share one git-facts read: stage/unstage/discard/commit
  and Refresh re-read it, and a git bar action re-reads the diff, the
  history and the file tree.
- The git bar no longer commits: the panel's staged-only box is the one
  commit path. Orphaned gitBar.commit*/cancel strings removed (en, vi).
- "New lane here" is wired from Workspace to the panel.

client/src/pages/Workspace.tsx

@@ -882,10 +882,6 @@ export function Workspace() {
                       (l) => l.source_repo === currentLane.cwd && l.id !== currentLane.id
                     )}
                     onSelectLane={setSelectedLaneId}
-                    onNewLaneFromRepo={(repo, branch) => {
-                      setAddLanePrefill({ sourceRepo: repo, branch });
-                      setAddLaneOpen(true);
-                    }}
                   />
                 </div>
                 <div className="mb-3">
@@ -1014,7 +1010,19 @@ export function Workspace() {
                     })()}
                   </button>
                 </div>
-                <LaneChangesPanel laneId={currentLane.id} />
+                <LaneChangesPanel
+                  laneId={currentLane.id}
+                  // A sibling worktree forks from the lane's SOURCE repo when
+                  // it has one (this lane is itself a worktree of it); an
+                  // adopted lane is its own repo.
+                  onNewLane={(branch) => {
+                    setAddLanePrefill({
+                      sourceRepo: currentLane.source_repo || currentLane.cwd,
+                      branch,
+                    });
+                    setAddLaneOpen(true);
+                  }}
+                />
               </aside>
             ) : (
               <button