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/styles/components.css

@@ -2460,6 +2460,15 @@
   overflow: hidden;
 }
 
+@keyframes settings-sub-section-flash {
+  0%   { border-color: var(--border-subtle); box-shadow: 0 0 0 0 color-mix(in srgb, var(--accent) 0%, transparent); }
+  20%  { border-color: var(--accent); box-shadow: 0 0 0 4px color-mix(in srgb, var(--accent) 35%, transparent); }
+  100% { border-color: var(--border-subtle); box-shadow: 0 0 0 0 color-mix(in srgb, var(--accent) 0%, transparent); }
+}
+.settings-sub-section--flash {
+  animation: settings-sub-section-flash 1.4s ease-out;
+}
+
 .settings-sub-section-summary {
   display: flex;
   align-items: center;
@@ -2591,10 +2600,6 @@
   color: var(--text-primary);
 }
 
-.settings-sub-section--hidden {
-  display: none;
-}
-
 .settings-search-empty {
   padding: var(--space-3) var(--space-4);
   font-size: 13px;
@@ -2605,31 +2610,18 @@
   text-align: center;
 }
 
-.settings-search-other-tabs {
-  margin-top: var(--space-4);
-  margin-bottom: var(--space-6);
+.settings-search-results {
+  list-style: none;
+  margin: var(--space-4) 0 var(--space-6);
   padding: var(--space-3);
   border-radius: var(--radius-md);
   background: var(--bg-card);
   border: 1px solid var(--border-subtle);
-}
-.settings-search-other-tabs-title {
-  font-size: 12px;
-  font-weight: 600;
-  text-transform: uppercase;
-  letter-spacing: 0.04em;
-  color: var(--text-muted);
-  margin-bottom: var(--space-2);
-}
-.settings-search-other-tabs-list {
-  list-style: none;
-  margin: 0;
-  padding: 0;
   display: flex;
   flex-direction: column;
   gap: 2px;
 }
-.settings-search-other-tab-item {
+.settings-search-result-item {
   width: 100%;
   display: flex;
   align-items: center;
@@ -2644,11 +2636,16 @@
   font-size: 13px;
   transition: background 0.12s, border-color 0.12s;
 }
-.settings-search-other-tab-item:hover {
+.settings-search-result-item:hover,
+.settings-search-result-item[data-selected="true"] {
   background: var(--bg-hover);
   border-color: var(--border);
 }
-.settings-search-other-tab-badge {
+.settings-search-result-item[data-selected="true"] {
+  border-color: var(--accent);
+  background: color-mix(in srgb, var(--accent) 8%, var(--bg-hover));
+}
+.settings-search-result-badge {
   flex-shrink: 0;
   font-size: 11px;
   font-weight: 500;
@@ -2657,7 +2654,7 @@
   background: color-mix(in srgb, var(--accent) 15%, transparent);
   color: var(--accent);
 }
-.settings-search-other-tab-title {
+.settings-search-result-title {
   flex: 1;
   min-width: 0;
   overflow: hidden;