web: the library's strip comes back drawing what it drew — the branch under the open folder, or only the folder, whichever the last visit chose

The strip's one switch, whole-branch or this-folder-only, was a plain useState and
started every visit deep. Every other thing this screen remembers — the open node,
the frame that was up, the column width, the rows left open — is kept by the same
helper under a key of its own; this one was left out. It gets a key, a default that
only a stored 'false' turns off, and the effect the others have.

docker/frontend/src/Library.tsx

@@ -64,6 +64,7 @@ const NODE_KEY = 'recipescam.library.node';
 const FRAME_KEY = 'recipescam.library.frame';
 const COLUMN_KEY = 'recipescam.library.column';
 const OPEN_KEY = 'recipescam.library.open';
+const DEEP_KEY = 'recipescam.library.deep';
 const COLUMN_MIN = 88;
 const COLUMN_MAX = 460;
 const COLUMN_DEFAULT = 118;
@@ -128,8 +129,9 @@ export function Library() {
   });
   // Whether the strip draws the whole branch under the open node or only the
   // node itself. Deep is how a roll reads — its top level holds no file of its
-  // own — and shallow is what a folder of folders is for.
-  const [deep, setDeep] = useState(true);
+  // own — and shallow is what a folder of folders is for. The reader's answer is
+  // picked up where the last visit left it, the same as the open node above.
+  const [deep, setDeep] = useState(() => recall(DEEP_KEY) !== 'false');
   // The frame that is up in the open node — raised by a click on its thumbnail,
   // and picked up where the last visit left it, so a reader who leaves for the
   // studio comes back to the negative they were looking at rather than to the
@@ -358,7 +360,8 @@ export function Library() {
   }, [reload]);
 
   // What the screen remembers: the folder that was open, the frame that was up in
-  // it, and the width its column was dragged to.
+  // it, the width its column was dragged to, and whether the strip drew the whole
+  // branch under that folder or only the folder itself.
   useEffect(() => {
     if (node) keep(NODE_KEY, node);
   }, [node]);
@@ -371,6 +374,9 @@ export function Library() {
   useEffect(() => {
     keep(OPEN_KEY, [...expanded].join(','));
   }, [expanded]);
+  useEffect(() => {
+    keep(DEEP_KEY, String(deep));
+  }, [deep]);
 
   // The menu closes on the next click anywhere but its own items, and on Escape.
   // Escape is the whole reason this listens on the document instead of sitting