Fix outline resume flow and PPTX export config

[Fang5237]

Summary

• make continue-from-stage return an explicit outline stream action so the browser actually resumes outline generation
• mark outline generation as running/failed across stream startup, provider errors, empty output, parse failures, and SSE error payloads
• load the Apryse Server SDK license from system config for PPTX export and pass the standard PPTX export gate into the editor route

Tests

• uv run pytest tests/test_project_workflow_regressions.py tests/test_sync_db_config_access.py::test_pdf_to_pptx_converter_license_key_uses_system_sync_db_config tests/test_sync_db_config_access.py::test_pdf_to_pptx_converter_uses_server_sdk_system_license_path tests/test_web_route_modularization.py::test_project_slides_editor_standard_pptx_export_gate_is_route_backed

Note

• uv run pytest tests/test_project_workflow_regressions.py tests/test_sync_db_config_access.py tests/test_web_route_modularization.py has one pre-existing failure on test_admin_env_editor_surface_was_removed_but_db_config_routes_remain: admin_routes.py already contains EnvFileUpdateRequest and /api/system-env-file routes on current master.

[Fang5237]

Added a follow-up commit to keep the AI edit stream responsive: the assistant message now renders a short status/summary instead of repeatedly laying out the full generated slide HTML during streaming.\n\nAdditional test run: \uv run pytest tests/test_project_workflow_regressions.py\ -> 16 passed.