fix: set root logger handler level on SIGHUP log_level reload

basicConfig creates a StreamHandler with its own level filter.
Changing only the logger levels left the handler filtering at the
original level, so debug messages were silently dropped after reload.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/s5p/server.py

@@ -267,9 +267,12 @@ async def serve(config: Config) -> None:
         config.retries = new.retries
         if new.log_level != config.log_level:
             config.log_level = new.log_level
-            logging.getLogger("s5p").setLevel(
-                getattr(logging, new.log_level.upper(), logging.INFO),
-            )
+            level = getattr(logging, new.log_level.upper(), logging.INFO)
+            root = logging.getLogger()
+            root.setLevel(level)
+            for h in root.handlers:
+                h.setLevel(level)
+            logging.getLogger("s5p").setLevel(level)
         if isinstance(proxy_pool, ProxyPool) and new.proxy_pool:
             await proxy_pool.reload(new.proxy_pool)
         logger.info("reload: config reloaded")