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/manual/index.html

@@ -148,7 +148,10 @@ is only about what you see.</p>
 <h2 id="opening-a-library">Opening a library</h2>
 <p>DarkRoom opens on a library: a folder on this machine, a folder a sync
 client keeps, or a Nextcloud account. A folder needs no password and uploads
-nothing.</p>
+nothing. <code>Choose folder…</code> opens your desktop's own folder dialogue, which can
+make a new folder too; the folder used last stays on the screen with
+<code>Open folder</code> beside it. On a Nextcloud account the library folder is chosen
+in a browser of the server, whose <code>New folder</code> makes one there.</p>
 <figure><img loading="lazy" src="media/launch.png" alt="The launch screen: a server field, a folder field, and which formats to scan for"><figcaption>The launch screen: a server field, a folder field, and which formats to scan for</figcaption></figure>
 <p>Once a folder is named, it is the library — you are not asked for it again,
 and <code>Open library</code> opens it whole. <code>Subfolder…</code> narrows the scan to part of
@@ -347,9 +350,22 @@ as the first step in its history.</p>
 <figure><img loading="lazy" src="media/panorama-filled.png" alt="The same, with the ragged border filled by the model rather than cropped away"><figcaption>The same, with the ragged border filled by the model rather than cropped away</figcaption></figure>
 <h2 id="export">Export</h2>
 <p><code>Export</code> in the develop header, or <code>Export N</code> from a selection. Format,
-size, colour space, sharpening, naming and where the file goes are in
-Settings, and apply to every export until changed. An export with no folder
-set is refused, and the header says so.</p>
+size, colour space, sharpening and naming are in Settings, and apply to every
+export until changed. Where the file goes is an album.</p>
+<p>An album is a folder exports go to, listed under <strong>Albums</strong> in the sidebar,
+below the collections. Press <code>+</code> there, or <code>New album…</code> in the export sheet
+(<code>Ctrl+E</code>), name it, and choose its folder: on this device, in the system's
+folder dialogue (on the tablet, Android's folder picker), or on the server,
+in a browser that can make a folder as well as open one. Not inside the
+library — a JPEG exported there would come back from the next scan as a
+photograph of its own, and the browser says so rather than letting you.</p>
+<p>The folder holds only the exported files. The album remembers which
+photograph each came from, so selecting it in the sidebar shows the
+originals behind its JPEGs — edit one and export it again. Albums reach your
+other devices as collections do; a folder on this device does not, so an
+album made on the desktop asks the tablet for a folder of its own. Deleting
+an album leaves its files where they are.</p>
+<p>An export with no album chosen is refused, and the header says so.</p>
 <figure><img loading="lazy" src="media/settings-export.png" alt="Export defaults in Settings"><figcaption>Export defaults in Settings</figcaption></figure>
 <h2 id="settings">Settings</h2>
 <figure><img loading="lazy" src="media/settings.png" alt="The settings page: background activity, indexing, storage, display"><figcaption>The settings page: background activity, indexing, storage, display</figcaption></figure>