fix: log exceptions on primary proxy target

When the primary request to llama-server (10.0.4.11:8081) raises an
exception (connection refused, timeout), it was silently swallowed by
the catch-all except block, making it look like a sidecar/switch
failure when it was actually a network-level error.

Now prints: 'PROXY EXCEPTION on primary <url>: <ExceptionType>: <msg>'

main.py

@@ -562,8 +562,11 @@ async def proxy(
     primary_result = None
     try:
         primary_result = await execute(target_url)
-    except Exception:
-        pass  # Falls through to fallback chain
+    except Exception as e:
+        print(
+            f"PROXY EXCEPTION on primary {target_url}: {type(e).__name__}: {e}",
+            flush=True,
+        )  # Falls through to fallback chain
     if primary_result is not None:
         return primary_result