Fix empty proxy sources (empty pool), first-run bat, elite hint

- load_settings/sanitize_settings: treat sources=[] as invalid; restore defaults (all([]) was true)
- _build_pool: defensive default sources + clearer empty-fetch log; elite-only empty fetch message
- FirstRun_Build_And_Install.bat: Python check + setup_and_build.ps1
- README + test for empty sources sanitize

Made-with: Cursor

tests/test_proxy_god.py

@@ -46,6 +46,13 @@ class TestConfig(unittest.TestCase):
         self.assertNotIn("secret", r)
         self.assertNotIn("alice", r)
 
+    def test_sanitize_restores_empty_sources(self) -> None:
+        s = Settings()
+        s.sources = []
+        s2, changed = sanitize_settings(s)
+        self.assertTrue(changed)
+        self.assertGreater(len(s2.sources), 0)
+
     def test_sanitize_clamps_extremes(self) -> None:
         s = Settings(
             chain_length=0,