[dfguerrerom]

Adds an opt-in TaskManager backend for SEPAL workspace exports, keeps ExportLauncher and direct GEE/Drive exports as they are, and moves to pysepal-api 0.4. Each TaskManager export builds a short-lived AsyncSepalClient from the session's SepalClient and closes it when done, so no async client is tied to a session or event loop. Backend options and workspace paths are checked before submission, and a failed submission never falls back to another backend: a 4xx is reported as a rejection with no task created, while network errors, 5xx and timeouts are reported as an unknown outcome.

Enable on supported deployments with PYSEPAL_TASKMANAGER_EXPORTS=1; the flag only affects the dialog, and in auto mode requests using priority, table max_vertices or a table format TaskManager rejects (such as TFRecord) stay on the direct path. The export dialog no longer lets users pick a Google Drive folder for SEPAL workspace exports, and the direct path now stages them in a fresh SEPAL/exports/<name>_<timestamp> Drive folder, as the SEPAL UI does, instead of searching and deleting by name across the user's whole Drive; the folder is removed after the copy or a definite failure, and kept when the outcome is unknown. GEE/Drive through TaskManager is a later phase.

Validation: nox -s test passes against pysepal-api 0.4.0 (1463 passed; the 3 test_gdal_env failures are the known nox-only ones).