feat(sources): externer Reputations-Layer (IFCN + EUvsDisinfo)

Externe Datenquellen (kostenlos, Open Data) ergaenzen die LLM-geschaetzte
Reliability-Achse mit objektiven Signalen:

- IFCN-Signatories (raw.githubusercontent.com/IFCN/verified-signatories):
  Plain-Text-Liste anerkannter Faktencheck-Organisationen.
- EUvsDisinfo (Zenodo CSV): Pro-Kreml-Desinformations-Datenbank.

Schema-Erweiterung:
- ifcn_signatory, eu_disinfo_listed, eu_disinfo_case_count,
  eu_disinfo_last_seen, external_data_synced_at.

Service src/services/external_reputation.py:
- sync_ifcn_signatories(), sync_eu_disinfo(), apply_reputation_overrides(),
  sync_all() mit Domain-Normalisierung (lowercase, ohne www., ohne Schema).

Reliability-Override-Regeln (laufen nach Approve und manuellem Sync):
- ifcn_signatory=1 -> reliability=sehr_hoch
- eu_disinfo_case_count >= 5 -> reliability=sehr_niedrig
- eu_disinfo_case_count >= 1 -> Reliability eine Stufe runter (max niedrig)

API: POST /api/sources/external-reputation/sync (Admin, BackgroundTask).
Filter: ?ifcn_signatory=true, ?eu_disinfo_listed=true.

UI:
- Filter-Dropdown "Externe Reputation" im Quellen-Modal.
- Badges: gruenes "IFCN" und rotes "EU-Desinfo (n)".
- Tooltip macht Reliability-Quelle transparent: "(IFCN-Faktenchecker)",
  "(EU-Desinfo, n Faelle)" oder "(LLM-Schaetzung)".
- "Externe Daten syncen"-Button im Review-Toolbar (Admin-only).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/static/js/app.js

@@ -2834,6 +2834,16 @@ async handleRefresh() {
         }
     },
 
+    async triggerExternalReputationSync() {
+        if (!confirm('IFCN- und EUvsDisinfo-Datenbanken jetzt syncen? Lauft im Hintergrund (~30 Sek).')) return;
+        try {
+            await API.triggerExternalReputationSync();
+            UI.showToast('Externer Sync gestartet. Quellenliste in 30 Sek neu laden.', 'info');
+        } catch (err) {
+            UI.showToast('Sync fehlgeschlagen: ' + err.message, 'error');
+        }
+    },
+
     renderSourceStats(stats) {
         const bar = document.getElementById('sources-stats-bar');
         if (!bar) return;
@@ -2866,6 +2876,7 @@ async handleRefresh() {
         const mediaTypeFilter = document.getElementById('sources-filter-mediatype')?.value || '';
         const reliabilityFilter = document.getElementById('sources-filter-reliability')?.value || '';
         const alignmentFilter = document.getElementById('sources-filter-alignment')?.value || '';
+        const externFilter = document.getElementById('sources-filter-extern')?.value || '';
         const search = (document.getElementById('sources-search')?.value || '').toLowerCase();
 
         // Alle Quellen nach Domain gruppieren
@@ -2929,6 +2940,11 @@ async handleRefresh() {
             if (alignmentFilter) {
                 if (!feeds.some(f => Array.isArray(f.alignments) && f.alignments.includes(alignmentFilter))) continue;
             }
+            if (externFilter === 'ifcn') {
+                if (!feeds.some(f => f.ifcn_signatory)) continue;
+            } else if (externFilter === 'eu_disinfo') {
+                if (!feeds.some(f => f.eu_disinfo_listed)) continue;
+            }
 
             // Suche
             if (search) {