feat(i18n): localize plugin catalog names and shell preset desc

Catalog entry names (15 tab + 4 viewer) and the dsh-desktop shell preset
desc were raw hardcoded zh strings rendered straight into the add-plugin
modals and the title-bar scheme dropdown. Mirror the existing desc
pattern exactly: PluginEntry.name / ShellPreset.desc widen to the
i18n-friendly string-or-() =>-string union, the catalogs carry lazy
t('pluginXxxName') / t('presetDshDesktopDesc') lookups, and the
add-plugin modal (render, search filter, aria-labels) plus the scheme
SelectMenu resolve them like every other copy. The plain-string arm of
the union stays as the raw-name fallback, and t() itself never yields
empty text (missing keys render the key), so a dict gap can never blank
a name.

20 new dictionary keys added to zh/en (locales.ts), ja (locales-ja.ts),
and all 18 third-language dictionaries — tests/locales.spec.ts enforces
key-set equality against zh for every shipped dict (precedent: 9cc642b),
so the 'leave other locales-* untouched' shortcut would fail the hard
parity gate; real translations are provided instead.

Spec follow-ups (behavior change: names/descs now render through t()):
- plugin-list.spec.ts: name non-empty assertion resolves the union.
- add-plugin-modal.spec.tsx: sentinel/office name assertions resolve
  from the catalog (en locale in tests) instead of pinning zh literals.
- shell-presets.spec.ts: desc non-empty assertion resolves the union.

src/client/locales-de.ts

@@ -407,4 +407,24 @@ export const de: Record<string, string> = {
   pluginDocsPanelDesc: '„Globale Dokumente“ in der DSH-Seitenleiste: eigene Markdown-Notizen aus jedem Arbeitsbereich lesen – Dateiliste, Gliederung, Öffnen in Chrome / VS Code und Kopieren-Buttons; das Dokumentenverzeichnis ist konfigurierbar (Standard ~/.dsh/docs)',
   pluginEgoBrowserDesc: 'Der Agent-Browser für DeepSeek Harness: 32 ego_*-Tools steuern ein echtes Chromium; ein nativer „ego-Browser“-Tab in der Seitenleiste zeigt live jede Seite, die der Agent besucht – Klicken, Ziehen und Tippen zum Übernehmen. Registriert den Tab automatisch, wenn better-sidebar vorhanden ist, sonst eine schwebende Blase',
   pluginBilingualReaderDesc: 'PDFs im DSH-Seitenbereich lesen: native PDF-Anzeige, Text auswählen und mit dem LLM übersetzen — mit Kontext, vollständig vom Hauptgespräch isoliert',
+  pluginSentinelName: 'dsh-sentinel Wecksystem',
+  pluginEgoBrowserName: 'ego-browser Agent-Browser',
+  pluginBetterOverleafName: 'dsh-better-overleaf Overleaf-Tab',
+  pluginDocsPanelName: 'dsh-docs-panel Globale Dokumente',
+  pluginFlowglassName: 'dsh-flowglass Flowglass',
+  pluginGitForgeName: 'dsh-git-forge Git-Zugangsdaten',
+  pluginGitRemotesName: 'dsh-git-remotes Git-Remotes',
+  pluginGithubWorkbenchName: 'dsh-github-workbench GitHub-Workbench',
+  pluginSidebarQaName: 'dsh-sidebar-qa Auswählen & Fragen',
+  pluginSidenoteName: 'dsh-sidenote Seiten-Chat',
+  pluginServerDeckName: 'dsh-server-deck Server-Deck',
+  pluginSuhuangScrollName: 'dsh-suhuang-scroll Suhuang Scroll',
+  pluginSshTunnelName: 'dsh-ssh-tunnel SSH-Tunnel',
+  pluginTurnReviewName: 'dsh-turn-review Runden-Review',
+  pluginBilingualReaderName: 'dsh-bilingual-reader Zweisprachiger Reader',
+  pluginOfficeName: 'Office-Vorschau',
+  pluginMdExportName: 'Markdown-Export',
+  pluginCodeNavName: 'Code-Vorschau-Navigation',
+  pluginVideoPreviewName: 'Video-Vorschau',
+  presetDshDesktopDesc: 'Elektronischer Erweiterte-Modus (rahmenlos): macOS reserviert oben 20px; Windows reserviert ohne WCO 32px für die Titelleiste',
 }