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

proxy_chain_manager/config.py

@@ -217,6 +217,10 @@ def sanitize_settings(s: Settings) -> tuple[Settings, bool]:
     except (TypeError, ValueError):
         s.validation_timeout_seconds = 12.0
         changed = True
+    # Empty list survives "all(isinstance…)" — would skip all fetches and yield an empty pool.
+    if not isinstance(s.sources, list) or not all(isinstance(x, str) for x in s.sources) or len(s.sources) == 0:
+        s.sources = list(Settings().sources)
+        changed = True
     return s, changed
 
 
@@ -240,8 +244,12 @@ def load_settings() -> Settings:
     for k, v in raw.items():
         if hasattr(s, k):
             setattr(s, k, v)
-    if not isinstance(s.sources, list) or not all(isinstance(x, str) for x in s.sources):
-        s.sources = Settings().sources
+    if (
+        not isinstance(s.sources, list)
+        or not all(isinstance(x, str) for x in s.sources)
+        or len(s.sources) == 0
+    ):
+        s.sources = list(Settings().sources)
     if s.obfuscation_mode not in OBFUSCATION_MODES:
         s.obfuscation_mode = "auto"
     if not isinstance(s.pinned_chain, list):