refactor(settings): thematic tab regroup + accordion sub-sections + in-page search (closes #257) (#259)

* refactor(settings): regroup tabs thematically + accordion sub-sections (progress on #257)

New tab structure: Servers (first) · Library · Audio · Lyrics · Appearance ·
Personalisation · Integrations · Input · Storage · System · Users.

Reusable SettingsSubSection (native <details>) wraps related settings per tab,
with an optional action slot for per-section reset buttons.

Moved:
- Lyrics sources + sidebar lyrics style → Lyrics
- Sidebar / artist layout / home customisers → Personalisation
- Last.fm / Discord / Bandsintown / Now-playing share → Integrations
  (with an opt-in privacy banner at the top)
- Tray / minimize / Linux smooth-scroll → System (new App-Verhalten group)
- Preload mini-player / custom titlebar / show artist images → Appearance visual options
- Language picker → System

Audio, Appearance and System tabs are now fully accordion-grouped.
Library tab reduced to Random Mix + Ratings accordions.
Servers tab is its own home (server cards + AudioMuse + logout) and the default
landing tab.

Indicators in the titlebar and offline banner route to the right tab.
EN + DE translations added for the new tab labels and privacy banner; other
locales fall back to English until the full i18n pass lands.

* refactor(settings): audio/input/storage/system accordions, in-page search, Navidrome focus

Settings refactor progress — every tab is now accordion-grouped:
- Audio: Output · Hi-Res · EQ · Playback · Next-track buffer
- Input: Keybindings · Global shortcuts (reset in accordion action slot)
- Storage: Offline · Downloads
- System: Language (default open) · Behavior · Backup · Logging · About · Contributors
- Contributors: own card grid with per-contributor expand, sorted by
  contribution count. Changelog accordion removed (release-notes link and
  "show changelog on update" toggle now live inside About).
- About: Navidrome focus; AI credit and Special Thanks removed; new
  Maintainers row (Psychotoxical + cucadmuh).

In-page search: magnifier icon next to the Settings title. Click opens a
240px search field. Filters the active tab's sub-sections by title match
(data-settings-search). Cross-tab search is tracked as a follow-up.

serverCompatible updated in all 8 locales from "Compatible with: Navidrome
Gonic Airsonic Subsonic" to a Navidrome-first wording that warns other
Subsonic-compatible servers may have reduced functionality.

Full i18n pass (tabLyrics/tabPersonalisation/tabIntegrations, aboutDesc,
privacy banner, etc. in fr/nl/zh/nb/ru/es) follows in a separate commit
after visual review.

* i18n(settings): complete localisation pass for refactored tabs

Added in all 8 locales (fr, nl, zh, nb, ru, es — en+de already in place):
- Tab labels: tabLibrary, tabServers, tabLyrics, tabPersonalisation, tabIntegrations
- inputKeybindingsTitle, searchPlaceholder, searchNoResults, aboutMaintainersLabel
- integrationsPrivacyTitle, integrationsPrivacyBody
- aboutContributorsCount_one/_other (ru also _few/_many for proper plural forms)
- aboutDesc rewritten to describe a Navidrome-focused player instead of a
  generic Subsonic-compatible one.

Removed dead keys in all 8 locales:
- aboutAiCredit, aboutSpecialThanksLabel — no longer rendered
- changelog — inline changelog accordion removed
- tabServer, tabGeneral — superseded by new tab structure

---------

Co-authored-by: Psychotoxical <dev@psysonic.app>

src/components/SettingsSubSection.tsx

@@ -0,0 +1,60 @@
+import React, { useId } from 'react';
+import { ChevronDown } from 'lucide-react';
+
+interface SettingsSubSectionProps {
+  title: string;
+  icon?: React.ReactNode;
+  defaultOpen?: boolean;
+  description?: string;
+  searchText?: string;
+  // Rechts im Summary neben dem Chevron (z.B. Reset-Button). Clicks werden
+  // gestoppt, damit sie das Accordion nicht togglen.
+  action?: React.ReactNode;
+  children: React.ReactNode;
+}
+
+// Wird innerhalb eines Settings-Tabs als Accordion-Gruppe genutzt. Natives
+// <details> liefert Keyboard + ARIA gratis; der CSS-Stil setzt den Chevron
+// im Summary mittels [open]-Selektor.
+export default function SettingsSubSection({
+  title,
+  icon,
+  defaultOpen = false,
+  description,
+  searchText,
+  action,
+  children,
+}: SettingsSubSectionProps) {
+  const headingId = useId();
+  return (
+    <details
+      className="settings-sub-section"
+      data-settings-search={searchText ?? title}
+      open={defaultOpen}
+    >
+      <summary
+        className="settings-sub-section-summary"
+        aria-labelledby={headingId}
+      >
+        {icon && <span className="settings-sub-section-icon">{icon}</span>}
+        <span id={headingId} className="settings-sub-section-title">{title}</span>
+        {action && (
+          <span
+            className="settings-sub-section-action"
+            onClick={e => e.stopPropagation()}
+            onKeyDown={e => e.stopPropagation()}
+          >
+            {action}
+          </span>
+        )}
+        <ChevronDown size={16} className="settings-sub-section-chevron" aria-hidden="true" />
+      </summary>
+      {description && (
+        <p className="settings-sub-section-desc">{description}</p>
+      )}
+      <div className="settings-sub-section-content">
+        {children}
+      </div>
+    </details>
+  );
+}