fix: visible-order range selection + preview-after-Space sequence

Two related bugs around visible vs API order.

1. Multi-select range selection (Shift+Click, Shift+Arrow):
- The previous selectRange walked the API photos array and only
  ADDED to the existing selection, never replacing or shrinking. So
  Shift+clicking to the left often "did nothing" (already-selected
  ids skipped) and the selection never matched the user's intended
  range.
- Replace with a store action that walks visiblePhotoIds (the visual
  row-major sequence Timeline already publishes), de-dupes ids
  (tag-grouped views can repeat photos), and REPLACES the selection.
- Track the range anchor as rangeStartId (a photo id) instead of an
  index so it survives filter changes and works correctly when API
  index != visual position.
- Drop the now-redundant lastSelectedIndex / globalIndex plumbing
  from selectPhoto / togglePhotoSelection — call sites simplify to
  pass just the photo id.

2. Preview navigation after pressing Space:
- The Space hotkey path called openPreview(id) without a sequence
  and relied on the store's fallback to whatever Timeline most
  recently published. Make it explicit: read visiblePhotoIds from
  the store snapshot at fire time and pass it through. Same effect
  in the happy case but eliminates any subtle publisher timing
  question.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/timeline/Timeline.tsx

@@ -166,10 +166,9 @@ export function Timeline() {
   const {
     selectedPhotos,
     activePhotoId,
-    lastSelectedIndex,
-    rangeStartIndex,
     selectPhoto,
     togglePhotoSelection,
+    selectRange,
     clearSelection,
     openPreview,
   } = usePhotoStore()
@@ -220,19 +219,6 @@ export function Timeline() {
     return result
   }, [items])
 
-  // Range-selection helper. Operates on the global photos array, not on
-  // virtualizer items.
-  const selectRange = (endIndex: number) => {
-    const startIndex = rangeStartIndex ?? lastSelectedIndex ?? 0
-    const minIndex = Math.min(startIndex, endIndex)
-    const maxIndex = Math.max(startIndex, endIndex)
-    for (let i = minIndex; i <= maxIndex; i++) {
-      if (i < photos.length && !selectedPhotos.includes(photos[i].id)) {
-        togglePhotoSelection(photos[i].id, i)
-      }
-    }
-  }
-
   // Virtual scrolling setup with per-item heights.
   const virtualizer = useVirtualizer({
     count: items.length,
@@ -384,9 +370,9 @@ export function Timeline() {
         const dest = photoRows[nextRow]?.cells[nextCol]
         if (!dest) return
         if (e.shiftKey) {
-          selectRange(dest.globalIndex)
+          selectRange(dest.photo.id)
         } else {
-          selectPhoto(dest.photo.id, dest.globalIndex)
+          selectPhoto(dest.photo.id)
         }
       }
 
@@ -410,9 +396,9 @@ export function Timeline() {
         case 'a':
           if (e.ctrlKey || e.metaKey) {
             e.preventDefault()
-            photos.forEach((photo, index) => {
+            photos.forEach((photo) => {
               if (!selectedPhotos.includes(photo.id)) {
-                togglePhotoSelection(photo.id, index)
+                togglePhotoSelection(photo.id)
               }
             })
           }
@@ -509,7 +495,7 @@ export function Timeline() {
                 }}
               >
                 <div className="flex" style={{ gap: `${GAP}px` }}>
-                  {item.cells.map(({ photo, globalIndex }) => (
+                  {item.cells.map(({ photo }) => (
                     <PhotoThumbnail
                       key={photo.id}
                       photo={photo}
@@ -517,12 +503,12 @@ export function Timeline() {
                       isSelected={selectedPhotos.includes(photo.id)}
                       isInActiveHeap={activeHeapMembers.has(photo.id)}
                       onClick={(e) => {
-                        if (e.shiftKey && lastSelectedIndex !== null) {
-                          selectRange(globalIndex)
+                        if (e.shiftKey) {
+                          selectRange(photo.id)
                         } else if (e.ctrlKey || e.metaKey) {
-                          togglePhotoSelection(photo.id, globalIndex)
+                          togglePhotoSelection(photo.id)
                         } else {
-                          selectPhoto(photo.id, globalIndex)
+                          selectPhoto(photo.id)
                         }
                       }}
                       onDoubleClick={() => openPreview(photo.id, visibleSequence)}