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.",

lib/l10n/app_en.arb

@@ -107,7 +107,14 @@
   "mcpSuggestionMemoryDesc": "Anthropic — persistent knowledge graph for an agent's memory.",
   "mcpSuggestionTimeDesc": "Anthropic — current time + timezone conversion.",
   "mcpServerEnLanguageBadge": "Server text in English — Studio shows it as supplied.",
-  "themePluginHeader": "Theme plugin",
+  "themePluginHeader": "Theme plugin (applies instantly)",
+  "themeApplied": "Theme applied: {name}",
+  "@themeApplied": {
+    "placeholders": {
+      "name": {"type": "String"}
+    }
+  },
+  "themePluginFailed": "Theme plugin could not load — keeping previous theme.",
   "themePluginNone": "Built-in (no plugin)",
   "themePluginHint": "Built-in and plugin tiles ship hand-curated palettes. The Custom tile derives a full Material 3 palette (primary, secondary, tertiary, surface, …) from one seed colour you pick — it's a complete theme, not a single-colour tweak.",
   "themePluginEmpty": "No theme plugins installed. Open the Store and pick one in the studio-plugin category.",
@@ -121,7 +128,7 @@
   "settingsHost": "Host",
   "settingsPort": "Port",
   "settingsTls": "TLS",
-  "settingsSaveAndConnect": "Save & connect",
+  "settingsSaveAndConnect": "Connect to endpoint",
   "settingsLanguage": "Language",
   "settingsLanguageHint": "App language. Affects every page; bilingual store entries also flip via this toggle.",
   "settingsHubEndpointHint": "Where should Studio connect? Default is the local hub at 127.0.0.1:50051.",

lib/l10n/app_localizations.dart

@@ -641,9 +641,21 @@ abstract class AppLocalizations {
   /// No description provided for @themePluginHeader.
   ///
   /// In en, this message translates to:
-  /// **'Theme plugin'**
+  /// **'Theme plugin (applies instantly)'**
   String get themePluginHeader;
 
+  /// No description provided for @themeApplied.
+  ///
+  /// In en, this message translates to:
+  /// **'Theme applied: {name}'**
+  String themeApplied(String name);
+
+  /// No description provided for @themePluginFailed.
+  ///
+  /// In en, this message translates to:
+  /// **'Theme plugin could not load — keeping previous theme.'**
+  String get themePluginFailed;
+
   /// No description provided for @themePluginNone.
   ///
   /// In en, this message translates to:
@@ -725,7 +737,7 @@ abstract class AppLocalizations {
   /// No description provided for @settingsSaveAndConnect.
   ///
   /// In en, this message translates to:
-  /// **'Save & connect'**
+  /// **'Connect to endpoint'**
   String get settingsSaveAndConnect;
 
   /// No description provided for @settingsLanguage.

lib/l10n/app_localizations_de.dart

@@ -313,7 +313,16 @@ class AppLocalizationsDe extends AppLocalizations {
       'Server-Text in Englisch — Studio zeigt ihn wie geliefert.';
 
   @override
-  String get themePluginHeader => 'Theme-Plugin';
+  String get themePluginHeader => 'Theme-Plugin (wirkt sofort)';
+
+  @override
+  String themeApplied(String name) {
+    return 'Theme aktiv: $name';
+  }
+
+  @override
+  String get themePluginFailed =>
+      'Theme-Plugin konnte nicht geladen werden — vorheriges Theme bleibt.';
 
   @override
   String get themePluginNone => 'Standard (kein Plugin)';
@@ -357,7 +366,7 @@ class AppLocalizationsDe extends AppLocalizations {
   String get settingsTls => 'TLS';
 
   @override
-  String get settingsSaveAndConnect => 'Speichern & verbinden';
+  String get settingsSaveAndConnect => 'Mit Endpoint verbinden';
 
   @override
   String get settingsLanguage => 'Sprache';

lib/l10n/app_localizations_en.dart

@@ -313,7 +313,16 @@ class AppLocalizationsEn extends AppLocalizations {
       'Server text in English — Studio shows it as supplied.';
 
   @override
-  String get themePluginHeader => 'Theme plugin';
+  String get themePluginHeader => 'Theme plugin (applies instantly)';
+
+  @override
+  String themeApplied(String name) {
+    return 'Theme applied: $name';
+  }
+
+  @override
+  String get themePluginFailed =>
+      'Theme plugin could not load — keeping previous theme.';
 
   @override
   String get themePluginNone => 'Built-in (no plugin)';
@@ -358,7 +367,7 @@ class AppLocalizationsEn extends AppLocalizations {
   String get settingsTls => 'TLS';
 
   @override
-  String get settingsSaveAndConnect => 'Save & connect';
+  String get settingsSaveAndConnect => 'Connect to endpoint';
 
   @override
   String get settingsLanguage => 'Language';