Specify albums and pointing at folders, and describe them in the manual

FR-EXP-10 is the album: a named export destination beneath the
collections, whose folder holds only the exported files while the
catalog links each back to its original; how albums sync, why a device
folder does not, and why the tables are made on first use rather than
by a migration. FR-EXP-6 now says the destination is an album, never
inside the library, and that folders are chosen by pointing — the
portal or Windows dialogue, SAF's tree picker, the server browser —
each able to make a folder.

The manual's launch and export sections say the same in the words on
screen. Its pictures still show the 0.16.0 launch screen and export
settings; they are re-recorded with the rig, not edited by hand.

docs/dev/requirements.md

@@ -867,8 +867,16 @@ full-size TIFF alongside a 2048px sRGB JPEG.
 
 **FR-EXP-6 — Naming and destination.** Output filenames are generated from a template supporting at
 minimum: original filename, sequence number, capture date, export dimensions, and preset name.
-Collision policy (overwrite / skip / auto-increment) is configurable. Destinations include a local
-path and a Nextcloud remote path (FR-NC-7).
+Collision policy (overwrite / skip / auto-increment) is configurable. The destination is an album
+(FR-EXP-10), whose folder is on this device or on the library's server (FR-NC-7) — never inside the
+library itself, where a scan would catalogue the exported files as photographs.
+
+A folder is chosen by pointing, never by typing a path: the platform's own dialogue on the desktop
+(the XDG desktop portal on Linux, which reaches the user's files from inside the Flatpak; the common
+item dialogue on Windows), the Storage Access Framework's tree picker on Android, and an in-app
+browser for a folder on the server. Every one of them can make a new folder as well as open one.
+The same applies to the other folders the application asks for on the desktop — the library folder,
+an import's source and second copy, and presets brought across from Lightroom.
 
 **FR-EXP-7 — Batch export.** Export a selection with one or more presets, running in the background
 with progress and cancellation. Uses all available cores and the GPU. A failure on one image is
@@ -881,6 +889,20 @@ strip GPS and personal metadata. Copyright and contact fields are settable per-p
 regardless of what the display was showing — including the high-quality demosaic (FR-RAW-3), never
 the fast preview method.
 
+**FR-EXP-10 — Albums.** An album is a named export destination listed in the library sidebar
+beneath the collections. Its folder holds only the exported files; the catalog records, for each
+file written there, the image it was rendered from, so that selecting the album shows the originals
+behind its files and re-exporting after an edit is one selection away. The export sheet chooses an
+album by name, and an export with no album chosen is refused and says so.
+
+Albums sync between devices as collections do (FR-CAT-7): by uuid and revision, deletions as
+tombstones, exports as a set union keyed on the server's file id. A folder on the server syncs with
+the album; a folder on the device does not, because a path or a SAF grant on one device means
+nothing on another — an album made elsewhere arrives with no folder here until one is chosen.
+Deleting an album never deletes the files in its folder. The album tables are created on first use
+rather than by a schema migration, so a device on an older build keeps merging the rest of the
+catalog.
+
 ### 3.7 Nextcloud integration
 
 Mechanics below are verified against Nextcloud 34 documentation and server/desktop-client source.