feat(ingest): --continuous flag on new-datasource (buckets) (#249)

* feat(ingest): --continuous flag on new-datasource (buckets)

Marks a bucket datasource for native continuous sync: the worker's scheduler
re-runs it incrementally, appending only newly-arrived objects. Adds
IngestRequest.continuous (serialized only when set) + the --continuous flag,
wired into the flag-driven filesystem builder and the wizard-skip check.
Server ignores it for non-filesystem families.

Test: --continuous rides through to the request body; default off is omitted
from the JSON.

* style: cargo fmt build_create_request continuous test assertion

---------

Co-authored-by: Eddie A Tejeda <669988+eddietejeda@users.noreply.github.com>

Author: eddietejeda