Build signed object URLs as path-only (/api/objects/...) instead of
prefixing APP_BASE_URL, so media loads from whatever host or reverse
proxy served the app. Remove the now-unused base URL from the signer and
drop the APP_BASE_URL / Server.BaseURL config.
Large albums opened slowly and flickered; the default album cover was
also lost in the media-objects refactor.
Large-album loading:
- quantize signed object URLs within a window and send Cache-Control so
previews are reused instead of re-fetched
- publish photo.updated (not photo.created) when variants are ready, so
clients update in place without reordering the grid
- worker concurrency + newest-first variant priority; raise default batch
Album cover:
- first uploaded photo becomes the cover when none is set
- clear the cover when the cover photo is trashed or moved out
- "set as album cover" in the photo context menu and actions panel
OpenSpec changes: fix-large-album-load, fix-album-cover
iu