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/widgets/fai_en_badge.dart

@@ -0,0 +1,61 @@
+// FaiEnBadge — small "[EN]" pill shown next to text that came
+// from outside Studio's localization pipeline (MCP server tool
+// names, n8n endpoint descriptions, native LLM responses).
+//
+// The honest move: when the active locale isn't English and we
+// show a piece of text that we know is English, mark it so the
+// operator doesn't blame Studio for a half-translated page.
+// `studio.translate` plugin will eventually rewrite these in
+// place — until then, the badge is the right amount of
+// transparency.
+
+import 'package:flutter/material.dart';
+
+import '../l10n/app_localizations.dart';
+import '../theme/tokens.dart';
+
+class FaiEnBadge extends StatelessWidget {
+  /// When true, the badge renders. When false (e.g. the active
+  /// locale already is English), it returns
+  /// `SizedBox.shrink()` so callers can drop it inline without
+  /// guarding visibility themselves.
+  final bool visible;
+
+  const FaiEnBadge({super.key, required this.visible});
+
+  /// Convenience constructor: derives `visible` from the active
+  /// Localizations locale. Use this from inside a Build method
+  /// where you already have a BuildContext.
+  factory FaiEnBadge.forContext(BuildContext context) {
+    final lang = Localizations.localeOf(context).languageCode;
+    return FaiEnBadge(visible: lang != 'en');
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    if (!visible) return const SizedBox.shrink();
+    final theme = Theme.of(context);
+    final l = AppLocalizations.of(context)!;
+    return Tooltip(
+      message: l.mcpServerEnLanguageBadge,
+      child: Container(
+        padding: const EdgeInsets.symmetric(horizontal: 6, vertical: 1),
+        decoration: BoxDecoration(
+          color: theme.colorScheme.surfaceContainerHighest,
+          borderRadius: BorderRadius.circular(FaiRadius.sm),
+          border: Border.all(
+            color: theme.colorScheme.outlineVariant,
+          ),
+        ),
+        child: Text(
+          'EN',
+          style: theme.textTheme.labelSmall?.copyWith(
+            fontSize: 9,
+            letterSpacing: 0.4,
+            color: theme.colorScheme.onSurfaceVariant,
+          ),
+        ),
+      ),
+    );
+  }
+}