fix(git): the branch switcher lists and checks out branches only the remote has

GET /api/lanes/:id/git/branches read only refs/heads, so a branch someone
else pushed never showed after a fetch or pull, and `switch` refused it
(ENOBRANCH). It now also returns `remotes`: fetched remote-tracking branches
with no local branch of that name (origin/HEAD left out), listed under
"On the remote"; switching to one runs `git switch -c <b> --track
refs/remotes/<remote>/<b>` with the remote ref looked up, never passed
through (bare name only when exactly one remote has it, else EAMBIGUOUS).
The bar also re-reads the branch list after a fetch or pull instead of
keeping the list it loaded first.

openapi.yaml

@@ -12276,8 +12276,8 @@ paths:
     get:
       tags:
         - Lanes
-      summary: The lane repo's own local branches
-      description: Feeds the lane's branch switcher. The repository comes from the lane row, never from the query — that is what GET /api/lanes/branches is for. Read-only, no same-origin guard.
+      summary: The lane repo's own local branches, and the remote ones not checked out yet
+      description: Feeds the lane's branch switcher. `branches` are the local branches; `remotes` the fetched remote-tracking branches with no local branch of that name yet (`origin/feature`, the remotes' HEAD left out) — `switch` to one creates its local tracking branch. The repository comes from the lane row, never from the query — that is what GET /api/lanes/branches is for. Read-only, no same-origin guard.
       operationId: listLaneOwnBranches
       parameters:
         - name: id
@@ -12287,7 +12287,7 @@ paths:
             type: integer
       responses:
         '200':
-          description: '{available, branches, current, worktrees}.'
+          description: '{available, branches, remotes, current, worktrees}.'
         '404':
           description: Lane not found.
   /api/lanes/{id}/git/commit-message: