Merge #2701@52ce53622 (photos dropped with no library open wait for one) into round3a-integration

crates/ui-egui/src/lib.rs: the batch's handle_dropped_files holds the photos
(library_problem::hold_dropped) before the Lightroom / running-import
checks. The drop card (drop_overlay.rs, LR-IMP-DRAGDROP) says the photos
wait instead of announcing an import or a review; test
photos_dropped_with_no_library_open_wait_for_one drops through
`ui.dropFiles`.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/control-protocol.md

@@ -166,7 +166,9 @@ catalog, a missing drive), the session starts empty and in memory — never with
 to do: `ui.inspect` → `libraryProblem` is `{path, error, temporarySession, pendingImport}` (else `null`); its buttons
 are `button:libraryRetry`, `button:libraryChoose`, `button:libraryTemporary` (Continue Without Saving) and
 `button:libraryQuit`. A temporary session shows a banner (`indicator:temporarySession`, `button:libraryReopen`) and
-writes nothing. `app.openLibrary` opening a library ends it.
+writes nothing. `app.openLibrary` opening a library ends it. `pendingImport` counts the files waiting for a
+library: those given on the command line, and photos dropped on the window while it (or the launch list below) is
+up; they are imported into the library that opens, or into the temporary session.
 
 ### Choosing the library at launch