Hover tooltips, clickable cross-references, easier highlighting

- Tooltips on hover and keyboard focus across the app: icon-only buttons show
  their label, existing titles show in the app's style without the browser's
  delay, and the reader's main buttons show shortcut hints ("Search (/)").
  Touch screens are unaffected.
- Reader: cross-references (under verses and in the Cross-refs tab) open the
  passage's text in the side panel without leaving the chapter; "Open chapter"
  goes there when wanted
- Reader: the verse panel now has a Highlight row of colours for one-tap
  whole-verse highlighting (tap again to remove, Clear for all, with Undo);
  selecting words still highlights just those
- Fix: a cross-reference preview was cleared when React ran the panel's
  effect twice (development builds)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/App.jsx

@@ -6,6 +6,7 @@ import { ToastProvider, useToast } from './components/Toasts.jsx';
 import CommandPalette from './components/CommandPalette.jsx';
 import ShortcutsHelp from './components/ShortcutsHelp.jsx';
 import SharedOutlineView from './components/SharedOutlineView.jsx';
+import Tooltips from './components/Tooltips.jsx';
 import { useAudio } from './hooks/useAudio.js';
 import { useAuth } from './hooks/useAuth.js';
 import { useBibleReader } from './hooks/useBibleReader.js';
@@ -437,6 +438,7 @@ const AppInner = () => {
       </Suspense>
       {paletteOpen && <CommandPalette onClose={() => setPaletteOpen(false)} />}
       {helpOpen && <ShortcutsHelp onClose={() => setHelpOpen(false)} />}
+      <Tooltips theme={reader.readerTheme} />
     </AppContext.Provider>
   );
 };