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>

API Server/panel/src/i18n/da.json

@@ -133,6 +133,7 @@
     "configure": "Konfigurer",
     "close": "Luk",
     "noConfig": "Dette plugin kræver ingen konfiguration.",
+    "notSet": "Ikke angivet — lad organisationer og brugere vælge",
     "capabilities": "Funktioner",
     "saved": "Gemt.",
     "checking": "Tjekker…",

API Server/panel/src/i18n/en.json

@@ -133,6 +133,7 @@
     "configure": "Configure",
     "close": "Close",
     "noConfig": "This plugin takes no configuration.",
+    "notSet": "Not set — let organizations and users choose",
     "capabilities": "Capabilities",
     "saved": "Saved.",
     "checking": "Checking…",

API Server/panel/src/i18n/pl.json

@@ -133,6 +133,7 @@
     "configure": "Konfiguruj",
     "close": "Zamknij",
     "noConfig": "Ta wtyczka nie wymaga konfiguracji.",
+    "notSet": "Nie ustawiono — pozwól organizacjom i użytkownikom wybrać",
     "capabilities": "Możliwości",
     "saved": "Zapisano.",
     "checking": "Sprawdzanie…",