ui(sidebar): pin heap, single scroll area, collapsible metadata group

The right sidepanel had three stacked flex regions (heap card +
header + PhotoInfoPanel) with PhotoInfoPanel maintaining its own
internal scroll. That made the editable fields (filename, title,
notes, rating, color, flag) stick at the top — separate from the
readonly metadata that scrolled below. Effectively two scroll
boundaries on one sidebar.

Move the scroll boundary up so only ActiveHeapCard + Header stay
pinned; editable fields and readonly metadata now scroll together.
Wrap the four readonly sections (Tags / Basic Info / Camera /
Location) in a single outer 'Metadata' collapsible so the user can
hide the whole block with one click. Sub-sections inside stay
individually collapsible.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/layout/RightSidebar.tsx

@@ -249,6 +249,9 @@ export function RightSidebar() {
   }
 
   // ── Single-photo: full editor via PhotoInfoPanel ────────────────────
+  // Heap card + header stay pinned at the top; the edit fields and
+  // readonly metadata sections scroll together in a single overflow
+  // region below.
   if (selectedPhotos.length === 1) {
     const id = activePhotoId ?? selectedPhotos[0]
     return (
@@ -259,7 +262,9 @@ export function RightSidebar() {
       >
         <ActiveHeapCard />
         <Header />
-        <PhotoInfoPanel photoId={id} />
+        <div className="flex-1 overflow-y-auto">
+          <PhotoInfoPanel photoId={id} />
+        </div>
       </div>
     )
   }

frontend/src/components/sidebar/PhotoInfoPanel.tsx

@@ -143,7 +143,7 @@ export function PhotoInfoPanel({ photoId, darkTheme = false }: PhotoInfoPanelPro
   const queryClient = useQueryClient()
 
   const [expandedSections, setExpandedSections] = useState<Set<string>>(
-    new Set(['basic', 'camera', 'location', 'tags'])
+    new Set(['metadata', 'basic', 'camera', 'location', 'tags'])
   )
   const toggleSection = (section: string) => {
     const next = new Set(expandedSections)
@@ -380,10 +380,13 @@ export function PhotoInfoPanel({ photoId, darkTheme = false }: PhotoInfoPanelPro
       : 'border-border bg-bg text-text placeholder-text-faint focus:border-primary'
   )
 
+  // Note: no h-full / flex-1 here — the parent (RightSidebar) owns the
+  // scroll container so the edit fields and readonly metadata scroll
+  // together as one block beneath the pinned heap + header.
   return (
     <div
       className={cn(
-        'flex h-full flex-col transition-opacity duration-150',
+        'flex flex-col transition-opacity duration-150',
         isPlaceholderData && 'opacity-70'
       )}
     >
@@ -542,8 +545,24 @@ export function PhotoInfoPanel({ photoId, darkTheme = false }: PhotoInfoPanelPro
         </div>
       </div>
 
-      {/* Read-only metadata sections */}
+      {/* Read-only metadata — collapsed/expanded as one block so the user
-      <div className="flex-1 overflow-y-auto">
+       *  can hide everything below the editable form with a single click.
+       *  Sub-sections inside stay individually collapsible for finer
+       *  control once the outer group is open. */}
+      <Collapsible
+        open={expandedSections.has('metadata')}
+        onOpenChange={() => toggleSection('metadata')}
+        className="border-b border-border"
+      >
+        <CollapsibleTrigger className="flex w-full items-center justify-between border-b border-border bg-surface-2/40 px-3 py-2 text-[11px] font-semibold uppercase tracking-[0.14em] text-text-muted hover:bg-surface-2 hover:text-text">
+          <span>Metadata</span>
+          {expandedSections.has('metadata') ? (
+            <ChevronDown className="h-3 w-3" />
+          ) : (
+            <ChevronRight className="h-3 w-3" />
+          )}
+        </CollapsibleTrigger>
+        <CollapsibleContent>
         <Section
           title="Tags"
           expanded={expandedSections.has('tags')}
@@ -667,8 +686,8 @@ export function PhotoInfoPanel({ photoId, darkTheme = false }: PhotoInfoPanelPro
             <div className="text-xs text-text-muted">No GPS data</div>
           )}
         </Section>
-
+        </CollapsibleContent>
-      </div>
+      </Collapsible>
     </div>
   )
 }