Stabilize Docker startup and runtime proxy

Reduce cold-start stalls by raising the default backend memory limit, bounding heavy feed concurrency, preserving non-empty startup caches, and refreshing working news feeds. Fix the Next API proxy for Docker control-plane writes by stripping unsupported hop/body headers and forwarding small request bodies safely. Keep the dashboard dynamic so production users do not get stuck on a cached startup shell.

backend/tests/test_news_keywords.py

@@ -145,6 +145,10 @@ class TestFeedConfig:
 
     def test_new_east_asia_feeds_present(self):
         names = {f["name"] for f in DEFAULT_FEEDS}
-        expected = {"FocusTaiwan", "Kyodo", "SCMP", "The Diplomat", "Stars and Stripes",
-                    "Yonhap", "Nikkei Asia", "Taipei Times", "Asia Times", "Defense News", "Japan Times"}
+        expected = {"SCMP", "The Diplomat", "Yonhap", "Asia Times", "Defense News", "Japan Times"}
         assert expected.issubset(names)
+
+    def test_known_dead_feeds_are_not_defaulted(self):
+        urls = {f["url"] for f in DEFAULT_FEEDS}
+        assert "https://www.reutersagency.com/feed/?best-topics=world" not in urls
+        assert "https://rsshub.app/apnews/topics/world-news" not in urls