chore: drop E shortcut for preview, keep only Space

E was a Lightroom holdover and overlapped with the natural rating /
flag culling shortcuts. Space is the only binding now (double-click on
a thumbnail still works). Hints pill updated.

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

frontend/src/components/KeyboardHints.tsx

@@ -13,14 +13,14 @@ export function KeyboardHints() {
         { key: '1-5', action: 'Rate' },
         { key: 'P', action: 'Pick' },
         { key: 'X', action: 'Discard' },
-        { key: 'E / Space', action: 'Preview' },
+        { key: 'Space', action: 'Preview' },
         { key: 'Esc', action: 'Deselect' },
       ]
     : [
         { key: '↑↓←→', action: 'Navigate' },
         { key: 'Click', action: 'Select' },
         { key: 'Shift+Click', action: 'Range' },
-        { key: 'E / Space', action: 'Preview' },
+        { key: 'Space', action: 'Preview' },
         { key: '\\', action: 'Filters' },
         { key: '/', action: 'Search' },
       ]

frontend/src/hooks/useKeyboardShortcuts.ts

@@ -75,8 +75,8 @@ export function useKeyboardShortcuts(props: KeyboardShortcutsProps) {
   useHotkeys('/', focusSearch, HK_OPTS)
   useHotkeys('mod+f', focusSearch, HK_OPTS)
 
-  // E and Space both toggle the preview view (open from grid, close from
-  // preview). Double-click on a thumbnail does the same.
+  // Space toggles the preview view (open from grid, close from preview).
+  // Double-click on a thumbnail does the same.
   const openPreviewFromGrid = () => {
     const id = usePhotoStore.getState().activePhotoId ?? getFirstPhotoId?.() ?? null
     if (id) openPreview(id)
@@ -87,7 +87,6 @@ export function useKeyboardShortcuts(props: KeyboardShortcutsProps) {
     else openPreviewFromGrid()
   }
 
-  useHotkeys('e', togglePreview, HK_OPTS, [isPreview, getFirstPhotoId])
   useHotkeys('space', togglePreview, HK_OPTS, [isPreview, getFirstPhotoId])
 
   // ── Culling shortcuts (work in both grid and preview) ────────────────────