Phase 18 (Verwaltung): fetch_strategy in CRUD + Edit-Modal

- migrations/2026-05-09e_fetch_strategy.py NEU: ALTER TABLE sources ADD COLUMN
  fetch_strategy. Pre-flagging fuer FT/WSJ/NZZ etc. (paywall) und Rheinische
  Post/Verfassungsschutz (googlebot).
- shared/services/source_health.py: gesynct vom Monitor (Phase-18-Code mit
  Retry-Logik + Strategien default/googlebot/paywall/skip).
- routers/sources.py: GlobalSourceCreate/Update um fetch_strategy
  (Pattern-Validation), SOURCE_UPDATE_COLUMNS + INSERT erweitert.
- dashboard.html: Edit-Modal hat jetzt Dropdown sourceFetchStrategy.
- sources.js: laedt + sendet fetch_strategy mit.

Cache-Buster 20260509c -> 20260509d.

src/static/js/sources.js

@@ -297,6 +297,7 @@ function editGlobalSource(id) {
   document.getElementById("sourceNotes").value = s.notes || "";
   document.getElementById("sourceLanguage").value = s.language || "";
   document.getElementById("sourceBias").value = s.bias || "";
+  document.getElementById("sourceFetchStrategy").value = s.fetch_strategy || "default";
   openModal("modalSource");
 }
 
@@ -324,6 +325,7 @@ function setupSourceForms() {
       notes: document.getElementById("sourceNotes").value || null,
       language: document.getElementById("sourceLanguage").value || null,
       bias: document.getElementById("sourceBias").value || null,
+      fetch_strategy: document.getElementById("sourceFetchStrategy").value || "default",
     };
 
     try {