Fix interface naming and save command for BOSS v7.9.6

- Use FastEthernet {p} instead of GigabitEthernet {p} for interface commands
- Use save config instead of copy running-config nvram:config.cfg

https://claude.ai/code/session_01JR2EMK7rwrZJowpstcaxQ6

switch_backend.py

@@ -393,7 +393,7 @@ def push_one_by_one(commands: list[str]) -> dict:
         _run_one(ch, "end")
         saved = False
         if stopped_at is None:
-            _, save_err = _run_one(ch, "copy running-config nvram:config.cfg")
+            _, save_err = _run_one(ch, "save config")
             saved = not save_err
             if saved:
                 log.info("Config saved to NVRAM")
@@ -607,7 +607,7 @@ def build_port(cfg: PortConfig) -> list[str]:
     Returns a list of CLI command strings ready for push_one_by_one().
     """
     p = cfg.port
-    iface = f"GigabitEthernet {p}"
+    iface = f"FastEthernet {p}"
     cmds = []
     if cfg.description:
         cmds += [f"interface {iface}", f'  name "{cfg.description}"']