Sidebar: group nav into priority-ordered functional sections

Turn the flat sidebar into a data-driven nav: each entry declares a
group (workspace/extensions/config/dev) and a numeric priority, and each
section renders by sorting on that key. Split axis is function, not
permission — adminOnly/debugOnly gate individual entries and an empty
section is hidden, so Configuration vanishes for non-admins without a
section-level role check.

- Shared folders moves into 'Your space' (still admin-gated per-entry).
- Plugin pages merge into the workspace group on the same priority line
  (>=100 by default); rebase the two in-repo plugins accordingly.
- Configuration and Development are collapsible, closed by default,
  state persisted in localStorage. Simple mode unchanged.
- Rename nav.catalog to 'Connectors Catalog' to disambiguate from the
  Plugin Catalog; add nav.section.* header keys (en/it/fr).
- Replace dead .sidebar-section-toggle CSS with real section classes.

web/i18n/it.js

@@ -1,5 +1,9 @@
 export default {
   // ── Navigazione ────────────────────────────────────────────────────────────
+  'nav.section.workspace':  'Il tuo spazio',
+  'nav.section.extensions': 'Estensioni',
+  'nav.section.config':     'Configurazione',
+  'nav.section.dev':        'Sviluppo',
   'nav.chat':          'Chat',
   'nav.inbox':         'Richieste',
   'nav.dashboard':     'Dashboard',
@@ -18,7 +22,7 @@ export default {
   'nav.connectors':    'Connettori',
   'nav.plugins':       'Plugin',
   'nav.plugin_catalog': 'Catalogo plugin',
-  'nav.catalog':       'Catalogo',
+  'nav.catalog':       'Catalogo connettori',
   'nav.config':        'Impostazioni',
   'nav.llm_requests':  'Richieste LLM',
   'nav.tic':           'Sessioni TIC',