Ports upstream C# e0e198e2 (SavePhotosToTimelineAsync, itself the JS
saveToTimeline). Photos already on our photos volume are moved into the
timeline root via PUT photos/volumes/{vid}/links/transfer-multiple,
batched so no request carries more than ten links and a photo is never
split from its related photos; photos on another volume — from an album
shared with us — are copied via POST volumes/{vid}/links/{lid}/copy, one
request each. That closes the cross-volume copy hole (TS copyPhoto).
The re-encryption is what add_photos_to_album already did, so it moves
into a shared photo_target_payload: name re-encrypted to the target key
and signed by the photos membership address, name/content hashes under
the target hash key, node passphrase rewrapped so the original
NodePassphraseSignature survives.
A photo the server reports an incomplete group for is re-queued once
with the related photos it named; only its second answer becomes an
outcome, so outcomes arrive in completion order, not input order.
Also adds ProtonPhotosClient::enumerate_events (c8d03244's only
non-interop hunk) and bumps the upstream pin to c8d03244. Upstream
29e58378 (upload telemetry) and 0537d906 (NodeProvider refactor) are
deliberately not ported — see UPSTREAM_SYNC.md.
nvrl