Split Web App Settings into tabs; allow unset plugin Control mode

Web App: Settings is now two tabs — Personal settings (account,
appearance, profile, privacy, advanced/danger) and Integrations
(Toyota, Anker Solix). Panels use v-show so loaded state and in-flight
edits survive a tab switch. Adds settings.tabs.* labels (en/pl/da).

API Server panel: non-required select config fields now render a
leading "Not set" option, so a superadmin can leave the Anker Solix
Control mode (and Toyota Brand) unset at the global layer. Previously
every option was a real value, forcing a pick that won the cascade and
locked organizations and users out of choosing their own mode. The
server side already treated an empty value as "abstain"; this closes
the UI gap. Adds plugins.notSet label (en/pl/da) and rebuilds the
embedded panel dist.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Web App/web/src/i18n/da.json

@@ -134,6 +134,10 @@
     "eyebrow": "Konto",
     "title": "Indstillinger",
     "subtitle": "Administrer din konto, udseende og dine data.",
+    "tabs": {
+      "personal": "Personlige indstillinger",
+      "integrations": "Integrationer"
+    },
 
     "account": {
       "title": "Konto",