fix(l10n): one term for capabilities, plain federation language

- 'Fähigkeiten' is the German lead term everywhere (welcome step 2,
  integrations panel, federation) — English jargon only as a
  parenthesized technical term on first mention
- 'Enrollment-Token' -> 'Registrierungs-Token', bootstrap label in
  plain words, CA spelled out, enrollment hint now formal address
- formality guard also rejects reader-addressed imperatives

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

lib/l10n/app_localizations_en.dart

@@ -257,11 +257,11 @@ class AppLocalizationsEn extends AppLocalizations {
       'Settings → System AI. Required for the AI search and inline failure explanations.';
 
   @override
-  String get welcomeChecklistMcp => 'Add a public capability source';
+  String get welcomeChecklistMcp => 'Connect a public tool catalog';
 
   @override
   String get welcomeChecklistMcpHint =>
-      'Add an MCP source from the Store, or configure one under Settings → MCP Clients.';
+      'Connects a public tool catalog (the technical term is MCP) — its capabilities then appear in the Store. Add one there, or under Settings → MCP Clients.';
 
   @override
   String get welcomeChecklistModule => 'Install a text module';
@@ -2084,7 +2084,7 @@ class AppLocalizationsEn extends AppLocalizations {
 
   @override
   String doctorSummaryChain(int verified, int total) {
-    return '$verified/$total chain';
+    return '$verified of $total events verified';
   }
 
   @override