feat: QR PNG 생성 + vote URL resolver

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

app.py

@@ -11,8 +11,11 @@ import os
 import random as _rand
 import threading
 from datetime import datetime
+import socket
+from io import BytesIO
 from pathlib import Path
 
+import qrcode
 import streamlit as st
 
 DATA_PATH = os.environ.get(
@@ -200,6 +203,35 @@ def fmt_team(team, titles):
     return f"{team} — {t}" if t else team
 
 
+def make_qr_png(url: str, box_size: int = 20) -> bytes:
+    img = qrcode.make(url, box_size=box_size, border=2)
+    buf = BytesIO()
+    img.save(buf, format="PNG")
+    return buf.getvalue()
+
+
+def _detect_lan_ip() -> str:
+    """LAN IP 자동 감지. 실패 시 'localhost'."""
+    try:
+        s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+        s.connect(("8.8.8.8", 80))
+        ip = s.getsockname()[0]
+        s.close()
+        return ip
+    except Exception:
+        return "localhost"
+
+
+def compute_vote_url() -> str:
+    data = load_data()
+    base = (
+        data.get("settings", {}).get("public_base_url")
+        or os.environ.get("PUBLIC_BASE_URL")
+        or f"http://{_detect_lan_ip()}:8501"
+    )
+    return f"{base.rstrip('/')}/?mode=vote"
+
+
 def compute_winners():
     """우선순위 기반 1팀 1상 + 동률 처리."""
     data = load_data()

tests/e2e.py

@@ -299,6 +299,38 @@ def t_topics_seeded_after_assign():
         assert c["tone"]
 
 
+def t_make_qr_png():
+    from app import make_qr_png
+    png = make_qr_png("http://localhost:8501/?mode=vote")
+    # PNG signature 8 bytes
+    assert png[:8] == b"\x89PNG\r\n\x1a\n"
+    assert len(png) > 100
+
+
+def t_compute_vote_url_priority():
+    import os as _os
+    from app import compute_vote_url, save_data, load_data, _empty_state
+    save_data(_empty_state())
+
+    # 1. settings.public_base_url 우선
+    d = load_data()
+    d["settings"]["public_base_url"] = "http://example.com:9000"
+    save_data(d)
+    assert compute_vote_url() == "http://example.com:9000/?mode=vote"
+
+    # 2. env fallback
+    d["settings"].pop("public_base_url")
+    save_data(d)
+    _os.environ["PUBLIC_BASE_URL"] = "http://env-host:7777"
+    assert compute_vote_url() == "http://env-host:7777/?mode=vote"
+    _os.environ.pop("PUBLIC_BASE_URL")
+
+    # 3. localhost / LAN fallback
+    url = compute_vote_url()
+    assert url.endswith("/?mode=vote")
+    assert url.startswith("http://")
+
+
 if __name__ == "__main__":
     print(f"# E2E (data={TEST_DATA})\n")
     test("hackathon.json 로드 (34명, 7팀)", t_load)
@@ -318,6 +350,8 @@ if __name__ == "__main__":
     test("stage 헬퍼", t_stage_helpers)
     test("topics 헬퍼", t_topics_helpers)
     test("topics 시드", t_topics_seeded_after_assign)
+    test("QR PNG 생성", t_make_qr_png)
+    test("vote URL 우선순위", t_compute_vote_url_priority)
 
     fails = sum(1 for r, _ in results if r == FAIL)
     print(f"\n# {len(results)} 중 통과 {len(results) - fails}, 실패 {fails}")