Validate hotkeys and support Super alias

src/hotkey.py

@@ -0,0 +1,30 @@
+from __future__ import annotations
+
+HOTKEY_MODIFIERS = {
+    "shift",
+    "ctrl",
+    "control",
+    "alt",
+    "mod1",
+    "super",
+    "mod4",
+    "cmd",
+    "command",
+}
+
+
+def split_hotkey(hotkey: str) -> tuple[list[str], str]:
+    parts = [p.strip() for p in hotkey.split("+") if p.strip()]
+    modifiers: list[str] = []
+    key_part = ""
+    for part in parts:
+        low = part.lower()
+        if low in HOTKEY_MODIFIERS:
+            modifiers.append(low)
+            continue
+        if key_part:
+            raise ValueError("must include exactly one non-modifier key")
+        key_part = part
+    if not key_part:
+        raise ValueError("missing key")
+    return modifiers, key_part