feat(settings): results-only search, keyboard nav, flash animation, Ctrl+F (#264)

Follow-up on #263. Refines the cross-tab search into a proper
command-palette-ish flow and polishes the UX around it.

Results-only mode:
- When a query is active, the tab content is hidden entirely; the
  results list is the only thing shown. Unified list (was: in-place
  current-tab filter + "In other tabs" panel underneath), sorted with
  current-tab matches first and then by score.
- Removed the DOM-based hide/show logic and its CSS helper class, the
  dead searchOtherTabs i18n key, and the searchHits/otherTabHits state.

Keyboard navigation inside the search field:
- ↓/↑ moves selection through the result list (clamped, no wrap).
- Enter activates the selected item (same flow as a click — clears
  query, switches tab, scrolls + opens + flashes the target).
- Mouse hover syncs with the keyboard selection so the two input modes
  don't fight each other.
- Selected item gets accent-border + tinted background; scrollIntoView
  with block:'nearest' keeps it visible when the list is long.

Ctrl/Cmd+F (Settings page only):
- Window keydown listener registered on mount, removed on unmount →
  the shortcut is live only while Settings is rendered.
- Opens the search input, focuses + selects it even if already open.
- preventDefault blocks the native WebKit find bar.
- Placeholder now hints at the shortcut: "… (Ctrl+F)" / "… (⌘F)" on
  macOS, no new i18n keys needed.

Target flash animation:
- After navigating from a result, the target SettingsSubSection gets a
  1.4s accent-colored border + glow pulse so the user immediately sees
  which entry the result pointed at. Reflow trick lets it retrigger
  when clicking the same result twice.

Misc:
- "Next Track Buffering" → "Buffering" in all 8 locales + the section
  comment in Settings.tsx. The SETTINGS_INDEX keeps "next track" as a
  keyword so old search habits still find it.

Co-authored-by: Psychotoxical <dev@psysonic.app>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/locales/de.ts

@@ -708,7 +708,6 @@ export const deTranslation = {
     aboutContributorsCount_other: '{{count}} Beiträge',
     searchPlaceholder: 'Einstellungen durchsuchen…',
     searchNoResults: 'Keine Treffer für deine Suche.',
-    searchOtherTabs: 'In anderen Tabs',
     integrationsPrivacyTitle: 'Hinweis zum Datenschutz',
     integrationsPrivacyBody: 'Alle Integrationen auf diesem Tab sind <strong>Opt-in</strong> und senden, sobald aktiviert, Daten an externe Dienste oder an deinen Navidrome-Server. Last.fm erhält deinen Wiedergabeverlauf, Discord zeigt den aktuell laufenden Track in deinem Profil an, Bandsintown wird pro Künstler für Tour-Daten abgefragt, und der „Jetzt läuft"-Hinweis veröffentlicht deinen aktuellen Titel für andere Benutzer deines Navidrome-Servers. Wer das nicht möchte, lässt den jeweiligen Abschnitt einfach deaktiviert.',
     homeCustomizerTitle: 'Startseite',
@@ -795,7 +794,7 @@ export const deTranslation = {
     gaplessDesc: 'Nächsten Track vorpuffern um Lücken zwischen Songs zu vermeiden',
     preloadMode: 'Nächsten Track vorpuffern',
     preloadModeDesc: 'Wann mit dem Puffern des nächsten Tracks begonnen werden soll',
-    nextTrackBufferingTitle: 'Nächster Track – Pufferung',
+    nextTrackBufferingTitle: 'Pufferung',
     preloadHotCacheMutualExclusive: 'Preload und Hot Cache erfüllen denselben Zweck – nur eine Methode kann gleichzeitig aktiv sein. Das Aktivieren einer deaktiviert die andere automatisch.',
     preloadOff: 'Aus',
     preloadBalanced: 'Ausgewogen (30 s vor Ende)',