fix(store,doctor): doc-verifier findings on the trust surfaces

The doc-verifier pass over the new trust/exposure surfaces came back
PASS with five improvements, all applied:
- the store policy notice gains a 'Learn more' into the security doc
  (the notice named security.require_signatures but not where it
  lives)
- 'blocked' disables the trust gate's install button — an active
  button contradicted the 'install would be refused' statement right
  above it (guard test added)
- the unknown-exposure tooltip now says what the operator can do
  (check where the name resolves)
- dead l10n key verifPillUnverified removed (unverified is the
  page-level notice, never a card pill)
- stale header comment in install_verification.dart corrected

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

lib/l10n/app_localizations_de.dart

@@ -2167,7 +2167,7 @@ class AppLocalizationsDe extends AppLocalizations {
 
   @override
   String get svcExposureUnknownHint =>
-      'Hostname statt IP-Adresse — der Hub löst zur Einstufung bewusst keine Namen auf.';
+      'Hostname statt IP-Adresse — der Hub löst zur Einstufung bewusst keine Namen auf. Prüfen Sie selbst, wohin der Name zeigt.';
 
   @override
   String get doctorLinkStore => 'Store öffnen';
@@ -2910,9 +2910,6 @@ class AppLocalizationsDe extends AppLocalizations {
   String get storePolicyUnverifiedNotice =>
       'Die Signaturpflicht ist in der Hub-Richtlinie ausgeschaltet — Installationen werden nicht kryptografisch geprüft. Der Installations-Dialog zeigt den Status je Modul; für geprüfte Installationen security.require_signatures aktivieren.';
 
-  @override
-  String get verifPillUnverified => 'unsigniert';
-
   @override
   String get verifPillBlocked => 'blockiert';