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.dart

@@ -3725,7 +3725,7 @@ abstract class AppLocalizations {
   /// No description provided for @svcExposureUnknownHint.
   ///
   /// In en, this message translates to:
-  /// **'Hostname instead of an IP address — the hub deliberately does not resolve names to classify.'**
+  /// **'Hostname instead of an IP address — the hub deliberately does not resolve names to classify. Check yourself where the name resolves.'**
   String get svcExposureUnknownHint;
 
   /// No description provided for @doctorLinkStore.
@@ -4940,12 +4940,6 @@ abstract class AppLocalizations {
   /// **'Signature enforcement is switched off in the hub policy — installs are not cryptographically verified. The install dialog shows the per-module status; enable security.require_signatures for verified installs.'**
   String get storePolicyUnverifiedNotice;
 
-  /// No description provided for @verifPillUnverified.
-  ///
-  /// In en, this message translates to:
-  /// **'unsigned'**
-  String get verifPillUnverified;
-
   /// No description provided for @verifPillBlocked.
   ///
   /// In en, this message translates to: