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/plugins-shared.ts

@@ -14,8 +14,10 @@ export const PLUGIN_TOPIC_URL = 'https://github.com/topics/dsh-better-sidebar'
 export interface PluginEntry {
   /** Unique id (the npm package name). */
   id: string
-  /** Short display name. */
-  name: string
+  /** Short display name (i18n friendly: string or () => string — the plain
+   *  string form is the raw-name fallback when no dictionary key covers the
+   *  entry, mirroring `description`). */
+  name: string | (() => string)
   /** GitHub repository URL. */
   url: string
   /** One-line description (i18n friendly: string or () => string). */