Import into the library, which is on the server

There was a local destination, defaulting to ~/Pictures, and an "upload" switch
that could be turned off. That was wrong twice over. DarkRoom's library *is* a
folder on a Nextcloud server (FR-NC-6) — there is no local library — so a
user-chosen local destination built a second pile of photographs that no view
in the application ever lists, and made "where did my import go" a question
with two answers.

An import now has exactly one destination and the page asks nothing about it.
With no account there is nowhere to go at all, so Import is refused rather than
quietly filling a folder.

What lands on the device is a staging copy in a directory the app owns, the
same shape `export` uses for its outbox and for the reason its module docs
give: staging first is the only path, not a fallback for being offline. The
bytes have to reach disk before the network — streaming a card straight to the
server would let a move-import erase a card against an in-flight upload, and
would make importing impossible with no connection (FR-NC-10). A staged file is
removed once the server confirms it; one that is not confirmed stays queued, and
the next import drains it.

And the rule that was stated but never enforced: `retirable` was reported and
`dr_ingest::retire` was never called by anything, so a move-import silently
behaved as a copy. The card is now emptied by the worker, of exactly those
photographs the *server* has confirmed — not those merely written here, because
the staging copy is removed moments later and anything unconfirmed would then
exist nowhere at all.

FR-NC-7b said "copied locally first ... then queued for upload", which is a
staging area; it has been rewritten to say so in terms that do not also permit
what was built.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

ui/dr-ui/src/lib.rs

@@ -953,6 +953,7 @@ pub fn run(paths: Vec<PathBuf>) -> Result<()> {
                         // pushes, so a thumbnail made during an import is the
                         // one every other client gets.
                         thumbs: library::thumbs_dir(&session.server, &session.user_id),
+                        staging: import::staging_dir(&session.server, &session.user_id),
                     }),
                 })
             },