feat: stage 헬퍼 (get_stage, set_stage, can_accept_votes)

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

app.py

@@ -111,6 +111,29 @@ def set_voting_open(flag):
     update_data(_fn)
 
 
+VALID_STAGES = ("intro", "topics", "vote")
+
+
+def get_stage():
+    return load_data().get("settings", {}).get("current_stage", "intro")
+
+
+def set_stage(stage):
+    if stage not in VALID_STAGES:
+        raise ValueError(f"invalid stage: {stage!r}")
+
+    def _fn(data):
+        data["settings"]["current_stage"] = stage
+        if stage == "vote":
+            data["settings"]["voting_open"] = True
+    update_data(_fn)
+
+
+def can_accept_votes(data):
+    s = data.get("settings", {})
+    return s.get("current_stage") == "vote" and s.get("voting_open", False)
+
+
 def get_tie_breaks():
     return load_data().get("tie_breaks", {})