feat(signal_v2): scheduler + 5 unit tests

Time-window dispatcher: pre-market (07:00-09:00, 5min), market
(09:00-15:30, 1min), post-market (15:30-20:00, 5min), overnight skip
to next market day 07:00. Weekend + holiday detection via holidays.json.

Stub holidays.json with 13 dates. Task 6 will sync from
web-backend/stock/app/holidays.json.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

signal_v2/tests/test_scheduler.py

@@ -0,0 +1,41 @@
+"""Tests for scheduler interval logic."""
+from datetime import datetime
+
+import pytest
+
+from signal_v2.scheduler import _next_interval, _is_market_day, KST
+
+
+def _kst(year, month, day, hour, minute=0):
+    return datetime(year, month, day, hour, minute, tzinfo=KST)
+
+
+def test_next_interval_pre_market_5min():
+    now = _kst(2026, 5, 18, 8, 30)  # Monday 08:30
+    assert _next_interval(now) == 300
+
+
+def test_next_interval_market_open_1min():
+    now = _kst(2026, 5, 18, 10, 0)  # Monday 10:00
+    assert _next_interval(now) == 60
+
+
+def test_next_interval_post_market_5min():
+    now = _kst(2026, 5, 18, 17, 0)  # Monday 17:00
+    assert _next_interval(now) == 300
+
+
+def test_next_interval_overnight_skip_to_next_morning():
+    now = _kst(2026, 5, 18, 22, 0)  # Monday 22:00
+    interval = _next_interval(now)
+    # Next polling: Tuesday 07:00 (9 hours away)
+    assert 9 * 3600 - 60 < interval < 9 * 3600 + 60
+
+
+def test_next_interval_holiday_skip():
+    # 2026-05-05 어린이날 (Tuesday holiday)
+    now = _kst(2026, 5, 5, 10, 0)
+    assert _is_market_day(now) is False
+    interval = _next_interval(now)
+    # Next: 2026-05-06 (Wed) 07:00, ~21h away
+    assert 20 * 3600 < interval < 22 * 3600