feat(studio): store-side source filter, provenance pills, one-click recommended sources (v0.29.0)

The Store is now the centre of capability discovery — provider
configuration moves out of Settings into the Store itself.
Three changes work together:

1. Source filter chips next to the existing status chips:
   All sources / Native / MCP / n8n. Applied client-side after
   the hub returns results so toggling is instant. The result
   count and the "Clear filters" reset both account for the
   source filter too.

2. Per-card provenance pill (`_ProvenancePill`): shows whether
   each entry is native, mcp · <provider>, or n8n · <provider>
   so the operator can triage the source at a glance — same
   role the "verified" badge plays in commercial app stores.

3. `_RecommendedSourcesStrip` replaces the older
   `_FederationNudge`. Renders curated public MCP servers
   (DeepWiki, Semgrep) as one-click cards with an inline
   `[+ Add]` button — no Settings detour, no form. Both servers
   are HTTPS Streamable-HTTP, no API key, no subprocess.
   Useful AI was considered but its 340+ tools would drown the
   index — kept out of the curated list. The strip auto-hides
   the moment any federated entry exists.

Removed the now-orphaned storeFederationNudge* ARB keys.

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

lib/l10n/app_de.arb

@@ -177,9 +177,36 @@
   "@storeDocsErrorNetwork": { "placeholders": { "detail": { "type": "String" } } },
   "storeDocsErrorParse": "README ist kein gültiges UTF-8.",
   "storeDocsErrorGeneric": "README konnte nicht geladen werden.",
-  "storeFederationNudgeTitle": "Mehr Capabilities?",
-  "storeFederationNudgeBody": "MCP-Server oder n8n-Endpunkt unter Einstellungen → MCP-Clients / N8N-Endpunkte konfigurieren. Entdeckte Tools und Workflows tauchen hier als `mcp.<server>.<tool>`- und `n8n.<endpoint>.<workflow>`-Capabilities auf — jeder Anthropic-/Community-MCP-Server bringt mehrere auf einmal.",
-  "storeFederationNudgeButton": "Einstellungen öffnen",
+  "storeSourceLabel": "Quelle",
+  "storeSourceAll": "Alle Quellen",
+  "storeSourceNative": "Nativ",
+  "storeSourceMcp": "MCP",
+  "storeSourceN8n": "n8n",
+  "storeProvenanceNative": "nativ",
+  "storeProvenanceMcp": "mcp · {provider}",
+  "@storeProvenanceMcp": { "placeholders": { "provider": { "type": "String" } } },
+  "storeProvenanceN8n": "n8n · {provider}",
+  "@storeProvenanceN8n": { "placeholders": { "provider": { "type": "String" } } },
+  "storeRecommendedTitle": "Öffentliche Quelle hinzufügen — ein Klick",
+  "storeRecommendedBody": "Kuratierte MCP-Server über HTTPS erreichbar. Kein Subprozess, kein API-Key, kein Node. Föderierte Capabilities erscheinen sofort im Store.",
+  "storeRecommendedAddTooltip": "Hinzufügen und entdecken",
+  "storeRecommendedAdding": "Wird hinzugefügt…",
+  "storeRecommendedDeepWikiTagline": "GitHub-Repo-Doku-Suche (KI-gestützt)",
+  "storeRecommendedSemgrepTagline": "Security-Scanning für Code-Schwachstellen",
+  "storeProviderAddedToast": "{name} hinzugefügt — {n} {n, plural, =1{föderierte Capability} other{föderierte Capabilities}}.",
+  "@storeProviderAddedToast": {
+    "placeholders": {
+      "name": { "type": "String" },
+      "n": { "type": "int" }
+    }
+  },
+  "storeProviderAddFailed": "{name} konnte nicht hinzugefügt werden: {error}",
+  "@storeProviderAddFailed": {
+    "placeholders": {
+      "name": { "type": "String" },
+      "error": { "type": "String" }
+    }
+  },
 
   "auditTitle": "Protokoll",
   "auditNoEvents": "Noch keine Ereignisse",