fix(studio): theme picker confirms applied + surfaces load failures

Two operator-visible fixes prompted by 'I picked a theme but
nothing changed':

  - Theme picker tile taps now show a brief "Theme applied:
    <name>" snackbar — the picker applies themes instantly, so
    the operator needs a confirming cue. Slow `_pluginThemes`
    loads no longer read as "click did nothing".
  - `_pluginThemes` failures (plugin unreachable, manifest
    drift, etc.) write to `FaiLog` so `fai admin doctor` and
    Studio's inline log viewer can surface them. Previously
    swallowed silently, which is what made debugging this so
    miserable.
  - Settings dialog's primary button relabelled to
    "Connect to endpoint" (was "Save & connect") so operators
    don't mistake it for "save my theme choice". The theme
    selection persists at tile-tap time; the Settings dialog
    has nothing left to "save".
  - Theme section header gains an explicit "(applies instantly)"
    cue for the same reason.

Also fixes a pre-existing curly-braces lint in the n8n add-
endpoint dialog. Studio bumped to 0.62.1, editor pinned via
path override at 0.15.1.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/l10n/app_de.arb

@@ -104,7 +104,14 @@
   "mcpSuggestionMemoryDesc": "Anthropic — persistenter Knowledge-Graph als Agenten-Gedächtnis.",
   "mcpSuggestionTimeDesc": "Anthropic — aktuelle Uhrzeit + Zeitzonen-Konvertierung.",
   "mcpServerEnLanguageBadge": "Server-Text in Englisch — Studio zeigt ihn wie geliefert.",
-  "themePluginHeader": "Theme-Plugin",
+  "themePluginHeader": "Theme-Plugin (wirkt sofort)",
+  "themeApplied": "Theme aktiv: {name}",
+  "@themeApplied": {
+    "placeholders": {
+      "name": {"type": "String"}
+    }
+  },
+  "themePluginFailed": "Theme-Plugin konnte nicht geladen werden — vorheriges Theme bleibt.",
   "themePluginNone": "Standard (kein Plugin)",
   "themePluginHint": "Built-in- und Plugin-Kacheln bringen handkuratierte Paletten mit. Die Kachel „Eigene Farbe\" leitet aus einer gewählten Seedfarbe eine vollständige Material-3-Palette ab (primary, secondary, tertiary, surface, …) — das ist ein vollwertiges Theme, kein Einzelfarb-Tweak.",
   "themePluginEmpty": "Kein Theme-Plugin installiert. Im Store eines aus der Kategorie studio-plugin auswählen.",
@@ -118,7 +125,7 @@
   "settingsHost": "Host",
   "settingsPort": "Port",
   "settingsTls": "TLS",
-  "settingsSaveAndConnect": "Speichern & verbinden",
+  "settingsSaveAndConnect": "Mit Endpoint verbinden",
   "settingsLanguage": "Sprache",
   "settingsLanguageHint": "Sprache der App. Wirkt auf alle Seiten; mehrsprachige Store-Einträge folgen ebenfalls.",
   "settingsHubEndpointHint": "Wohin soll Studio sich verbinden? Standard ist der lokale Hub auf 127.0.0.1:50051.",