ServiceNotFoundError (→ 404) and ServiceConflictError (→ 409) replace the
"not found" / "already on" / "not on" substring checks in _map_mutation_error;
base ServiceMutationError still maps to 422. Fixes three pre-existing test
status-code assertions (201 vs 200 on POST endpoints).
- GET /topologies/services/{name}/schema serves the declared ServiceConfigField
metadata so the Inspector can auto-render forms.
- PUT /(topologies/{id}/)deckies/{decky}/services/{svc}/config persists the
validated dict (DB + compose); container untouched (Save).
- POST /(topologies/{id}/)deckies/{decky}/services/{svc}/apply persists then
force-recreates <decky>-<svc> so the new env takes effect (Apply, destructive).
- New engine helper update_service_config wires both fleet and topology paths
through the existing _persist_fleet_change / _rerender_topology_compose
machinery; emits decky.<name>.service_config_changed on the bus.
