feat(errors): classify the install 'no store entry' failure

Even with the honest install badge the hub error stays reachable
(stale store snapshot, race with a store refresh, older hub). The
friendly-error mapper now gives it its own headline plus a hint
naming the three acquisition paths — local module install, adding
the providing store, configuring the MCP/n8n integration — in EN
and DE, with the verbatim hub message kept copyable. Matcher unit
tests EN+DE guard the classification.

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

lib/l10n/app_localizations_en.dart

@@ -248,6 +248,13 @@ class AppLocalizationsEn extends AppLocalizations {
   String get errCapabilityNotInstalledHint =>
       'Open the flow\'s Text tab — the analyzer\'s Fix button installs the capability if it\'s in the store.';
 
+  @override
+  String get errNoStoreEntry => 'No store entry provides this capability.';
+
+  @override
+  String get errNoStoreEntryHint =>
+      'Three ways to get it: install a local module (chain install --link <path>), add the store that provides it (Settings → Stores), or configure the integration (MCP/n8n) that supplies it. If it was just published, refresh the Store page first.';
+
   @override
   String get welcomeDocClose => 'Close';