fix(sidebar): the room filter hides empty sections and says when nothing matches (#289)

A filter matching nothing left Favorites / Projects / Rooms / Low
Priority headers with nothing under them. While filtering, sections
without a match are hidden, and with no match at all the list shows
"No rooms match “…”" with a Clear filter button.

Fixes #289

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/app/pages/client/home/Home.tsx

@@ -255,6 +255,8 @@ function HomeCustomSection({
       return (localName ?? matrixName).toLowerCase().includes(query);
     });
   }, [mx, section.rooms, closed, roomsWithUnreadSet, selectedRoomId, filterQuery]);
+  // [Gitea #289] While filtering, a section with no matches is hidden.
+  if (filterQuery.trim() && items.length === 0) return null;
   // Sections are user-curated and small, so they render plainly — no
   // virtualizer per section (a late-mounted one never measured its scroller).
   return (
@@ -443,6 +445,26 @@ export function Home() {
     });
   }, [mx, sortedRooms, filterQuery]);
 
+  // [Gitea #289] While filtering, hide empty sections; with no match at all,
+  // say so instead of leaving bare headers.
+  const filtering = filterQuery.trim().length > 0;
+  const customSectionMatch = useMemo(() => {
+    if (!filtering) return true;
+    const query = filterQuery.toLowerCase();
+    const localNames = getLocalRoomNamesContent(mx);
+    return customSections.some((section) =>
+      section.rooms.some((rId) =>
+        (localNames.rooms[rId] ?? mx.getRoom(rId)?.name ?? '').toLowerCase().includes(query),
+      ),
+    );
+  }, [mx, customSections, filtering, filterQuery]);
+  const noFilterMatch =
+    filtering &&
+    !customSectionMatch &&
+    filteredFavoriteRooms.length === 0 &&
+    filteredRooms.length === 0 &&
+    filteredLowPriorityRooms.length === 0;
+
   const favVirtualizer = useVirtualizer({
     count: filteredFavoriteRooms.length,
     getScrollElement: () => scrollRef.current,
@@ -580,7 +602,7 @@ export function Home() {
                 />
               </Box>
             </NavCategory>
-            {favoriteRooms.length > 0 && (
+            {favoriteRooms.length > 0 && (!filtering || filteredFavoriteRooms.length > 0) && (
               <NavCategory>
                 <NavCategoryHeader>
                   <RoomNavCategoryButton
@@ -629,6 +651,30 @@ export function Home() {
                 notificationPreferences={notificationPreferences}
               />
             ))}
+            {noFilterMatch && (
+              <NavCategory>
+                <Box
+                  direction="Column"
+                  alignItems="Center"
+                  gap="200"
+                  style={{ padding: config.space.S400 }}
+                >
+                  <Text size="T300" priority="300" align="Center">
+                    No rooms match &ldquo;{filterQuery.trim()}&rdquo;
+                  </Text>
+                  <Button
+                    size="300"
+                    variant="Secondary"
+                    fill="Soft"
+                    radii="300"
+                    onClick={() => setFilterQuery('')}
+                  >
+                    <Text size="B300">Clear filter</Text>
+                  </Button>
+                </Box>
+              </NavCategory>
+            )}
+            {(!filtering || filteredRooms.length > 0) && (
               <NavCategory>
                 <NavCategoryHeader>
                   <RoomNavCategoryButton
@@ -749,7 +795,11 @@ export function Home() {
                     const selected = selectedRoomId === roomId;
 
                     return (
-                    <VirtualTile virtualItem={vItem} key={roomId} ref={virtualizer.measureElement}>
+                      <VirtualTile
+                        virtualItem={vItem}
+                        key={roomId}
+                        ref={virtualizer.measureElement}
+                      >
                         <RoomNavItem
                           room={room}
                           selected={selected}
@@ -764,7 +814,8 @@ export function Home() {
                   })}
                 </div>
               </NavCategory>
-            {lowPriorityRooms.length > 0 && (
+            )}
+            {lowPriorityRooms.length > 0 && (!filtering || filteredLowPriorityRooms.length > 0) && (
               <NavCategory>
                 <NavCategoryHeader>
                   <RoomNavCategoryButton