feat: japan node ranking and leftover route detection

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

py_modules/mudfish_decky/routes.py

@@ -0,0 +1,36 @@
+"""Detect and remove the per-node host routes Mudfish leaves behind after it stops."""
+import subprocess
+from typing import Optional
+
+
+def host_routes(route_text: str) -> set:
+    """Host routes (no prefix length, no proto, with a gateway) from `ip -4 route` output."""
+    routes = set()
+    for line in route_text.splitlines():
+        parts = line.split()
+        if not parts or "/" in parts[0] or parts[0] == "default":
+            continue
+        if "proto" in parts or "via" not in parts:
+            continue
+        routes.add(" ".join(parts))
+    return routes
+
+
+def leftover_routes(before: Optional[set], after_text: str) -> list:
+    """Host routes added since `before`, excluding tunnel routes. No snapshot means delete nothing."""
+    if before is None:
+        return []
+    added = host_routes(after_text) - set(before)
+    return sorted(r for r in added if " dev tap" not in f" {r}")
+
+
+def delete_routes(lines: list, run=subprocess.run) -> int:
+    deleted = 0
+    for line in lines:
+        try:
+            result = run(["ip", "route", "del", *line.split()], capture_output=True, timeout=5)
+        except Exception:
+            continue
+        if result.returncode == 0:
+            deleted += 1
+    return deleted