Tag the SAF export path FR-EXP-10 only, not FR-PLAT-AND-1

saf.rs and the export path's SAF branch shipped tagged FR-PLAT-AND-1,
and the matrix counted the requirement as covered. Its subject is the
library — reached through SAF grants — and Android still reaches a
library over a Nextcloud account or a folder path. What the SAF code
does is give an album a folder on the tablet, which is FR-EXP-10.

outstanding.md said the figure overstated it and should be read with
this one subtracted; it now says the tags were narrowed, and coverage
reads 161 of 192.

ui/dr-ui/src/saf.rs

@@ -1,6 +1,10 @@
-//! TRACES: FR-EXP-10 | FR-PLAT-AND-1
+//! TRACES: FR-EXP-10
 //! Android's Storage Access Framework, for an album's folder on the device.
 //!
+//! Export folders only. FR-PLAT-AND-1 asks for the *library* to be reached
+//! through SAF, and it still is not — a library on the tablet is a server —
+//! so this module does not claim it.
+//!
 //! The folder is chosen in the system's own picker, which can make a new
 //! folder too, and comes back as a tree URI with a persisted grant. Exports
 //! are then written into it through `DocumentsContract` — a tree URI is not a