Salvages #26496 by @aqilaziz. Adds branch_name column + CLI flag so
tasks with workspace_kind='worktree' can pin a target branch on
create. Schema migration added to _migrate_add_optional_columns.
- Task.branch_name field + DB column + migration
- create_task accepts branch_name kwarg
- hermes kanban create --branch <name> flag
- kanban show output includes 'Branch: <name>' when set
Cherry-picked the substantive commit (a7558cf27); the PR's tip was
an unrelated service-path-dirs commit. Resolved 2 INSERT-column-list
and show-output conflicts alongside main's session_id and
max_runtime_seconds additions; kept all three.
1733cb3a13