feat(studio): trust pass — friendly errors + store clarity + MCP i18n

Second half of the May-2026 trust pass. Drops the wall of
gRPC trailers from every error surface and makes the Store
honest about what is and isn't installable.

Friendly errors:

- New `friendlyError(Object, AppLocalizations)` mapper turns
  GrpcError + arbitrary throwables into a localised headline,
  optional recovery hint, and a verbatim detail string kept
  behind a "Show details" expander. Duck-typed on `.code` /
  `.message` so Studio doesn't have to depend on package:grpc
  directly.
- `FaiErrorBox` gains an `error:` constructor that runs the
  mapper. Every call site that used to render
  `snap.error.toString()` (flows, welcome, store) switches to
  it.
- 9 .arb entries per locale cover the gRPC codes we actually
  emit (INVALID_ARGUMENT, NOT_FOUND, ALREADY_EXISTS,
  PERMISSION_DENIED, FAILED_PRECONDITION, INTERNAL,
  UNAVAILABLE, UNAUTHENTICATED) plus copy/details affordances.
- `test/friendly_error_test.dart` — 6 unit tests for the
  mapper. Covers the mapping table, locale-switching, and the
  non-gRPC fallback so future regressions show up in CI.

Capability discovery:

- New `HubService.allCapabilities()` reads the kind-aware
  capability list (wasm + builtin + federated) and returns a
  Dart-side `CapabilityInfo` value type. The flow page's
  missing-dependency check uses it so `system.approval` and
  federated MCP/n8n tools count as "available" — fixes the
  Run button staying disabled forever.
- `HubService.listModules()` filters to kind=wasm so the
  Modules page doesn't sprout synthetic "system" entries that
  the operator can't uninstall.

Store clarity:

- New "Installable only" filter, on by default. Roughly 2/3
  of seed entries currently carry `status: planned`; the
  default view stops being noise.
- Featured-strip cards for planned modules now show a
  "Coming soon" pill instead of an empty action area.
- Main-grid cards for non-installable modules dim to 60%
  opacity so the eye lands on actionable cards first.
- Detail-sheet "Nicht installierbar" tooltip → inline hint
  box. The reason is visible without hovering.

MCP localisation:

- `_kMcpSuggestions` no longer holds 11 hardcoded English
  description strings. The `description` field is replaced
  with a `resolveDescription(AppLocalizations)` lookup that
  switches on the suggestion `name` to read the matching
  `mcpSuggestion*Desc` .arb key. EN + DE shipped.
- New `FaiEnBadge` widget renders a small `[EN]` pill when
  the active locale isn't English. Used next to MCP /
  federated store entries' tagline + description because
  the server supplies them in English and we can't translate
  on the fly yet — the badge is the honest signal until the
  planned `studio.translate` plugin lands.

Plus housekeeping: removed the unused `_keepImport` lint
escape in the test and the dangling library doc-comment in
`format.dart`.

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

lib/l10n/app_localizations_de.dart

@@ -237,6 +237,71 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get buttonCopied => 'Kopiert';
 
+  @override
+  String get buttonShowDetails => 'Details anzeigen';
+
+  @override
+  String get buttonHideDetails => 'Details ausblenden';
+
+  @override
+  String get storeInstallableOnly => 'Nur installierbare';
+
+  @override
+  String get storePillComingSoon => 'Bald verfügbar';
+
+  @override
+  String storeNotInstallableInline(String status) {
+    return 'Dieses Modul ist auf der Roadmap (Status: $status). Es gibt noch kein installierbares Bundle — Repository verfolgen für Updates.';
+  }
+
+  @override
+  String get mcpSuggestionDeepwikiDesc =>
+      'Öffentliches HTTPS — KI-gestützte Doku-Suche in GitHub-Repos. Kein Node, kein API-Key.';
+
+  @override
+  String get mcpSuggestionSemgrepDesc =>
+      'Öffentliches HTTPS — Security-Scanning von Code-Schwachstellen. Kein Node, kein API-Key.';
+
+  @override
+  String get mcpSuggestionFilesystemDesc =>
+      'Anthropic — Dateien in /tmp lesen / schreiben. Pfad vor dem Speichern anpassen.';
+
+  @override
+  String get mcpSuggestionFetchDesc =>
+      'Anthropic — beliebige HTTP(S)-URLs als Markdown abrufen.';
+
+  @override
+  String get mcpSuggestionGithubDesc =>
+      'Anthropic — Issues, PRs, Repo-Dateien. Braucht einen GitHub-PAT in der Env-Variable.';
+
+  @override
+  String get mcpSuggestionPuppeteerDesc =>
+      'Anthropic — Headless-Browser-Automation für Screenshots / Scraping.';
+
+  @override
+  String get mcpSuggestionPostgresDesc =>
+      'Anthropic — Read-only-SQL-Queries gegen eine Postgres-Datenbank. URL anpassen.';
+
+  @override
+  String get mcpSuggestionSqliteDesc =>
+      'Anthropic — Abfragen gegen eine lokale SQLite-Datei. Pfad anpassen.';
+
+  @override
+  String get mcpSuggestionBraveSearchDesc =>
+      'Anthropic — Websuche via Brave. API-Key erforderlich.';
+
+  @override
+  String get mcpSuggestionMemoryDesc =>
+      'Anthropic — persistenter Knowledge-Graph als Agenten-Gedächtnis.';
+
+  @override
+  String get mcpSuggestionTimeDesc =>
+      'Anthropic — aktuelle Uhrzeit + Zeitzonen-Konvertierung.';
+
+  @override
+  String get mcpServerEnLanguageBadge =>
+      'Server-Text in Englisch — Studio zeigt ihn wie geliefert.';
+
   @override
   String get settingsTitle => 'Hub-Endpunkt';
 
@@ -1324,6 +1389,67 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get flowsNoOutputs => 'Flow abgeschlossen ohne deklarierte Outputs.';
 
+  @override
+  String get errGeneric => 'Da ist etwas schiefgegangen.';
+
+  @override
+  String get errInvalidArgument => 'Ungültige Eingabe.';
+
+  @override
+  String get errInvalidArgumentHint =>
+      'Werte im Formular prüfen und erneut versuchen.';
+
+  @override
+  String get errNotFound => 'Nicht gefunden.';
+
+  @override
+  String get errNotFoundHint =>
+      'Das Angefragte ist nicht hier — entweder entfernt oder nie existiert.';
+
+  @override
+  String get errAlreadyExists => 'Existiert bereits.';
+
+  @override
+  String get errPermissionDenied => 'Berechtigung verweigert.';
+
+  @override
+  String get errPermissionDeniedHint =>
+      'Die Operator-Policy des Hubs blockiert diese Aktion. `~/.fai/config.yaml` prüfen.';
+
+  @override
+  String get errFailedPrecondition => 'Setup-Problem hat das blockiert.';
+
+  @override
+  String get errFailedPreconditionHint =>
+      'Der Hub konnte nicht weiter, weil etwas Vorausgesetztes fehlt. Details unten erklären was.';
+
+  @override
+  String get errInternal => 'Unerwarteter interner Fehler.';
+
+  @override
+  String get errInternalHint =>
+      'Hub-Logs unter `~/.fai/logs/` prüfen. Wenn das öfter passiert, bitte melden.';
+
+  @override
+  String get errUnavailable => 'Hub nicht erreichbar.';
+
+  @override
+  String get errUnavailableHint =>
+      'Sicherstellen, dass `fai serve` (oder `fai daemon start`) läuft und der Daemon-Endpunkt zu Studios Einstellungen passt.';
+
+  @override
+  String get errUnauthenticated => 'Authentifizierung erforderlich.';
+
+  @override
+  String get errUnauthenticatedHint =>
+      '`FAI_REGISTRY_TOKEN` setzen oder in den Einstellungen anmelden, dann erneut versuchen.';
+
+  @override
+  String get errCopyDetail => 'Detail kopieren';
+
+  @override
+  String get errDetailCopied => 'Detail in die Zwischenablage kopiert.';
+
   @override
   String get flowsOutputUnknown => 'Unbekannter Output-Payload-Typ.';