Fix weekend filter: use precise forex market hours (Fri 22:00–Sun 22:00 UTC)

The old `weekday() >= 5` check blocked all of Sunday, but the forex
market reopens Sunday 22:00 UTC (Sydney open). Now uses proper time-based
check so the bot fetches data and generates signals on Sunday evening.

test_all.py

@@ -1491,7 +1491,7 @@ def _():
 
 @test("SCAN_BUTTONS and SCAN_LOOKUP consistency")
 def _():
-    assert len(SCAN_BUTTONS) == 4  # 3 TFs + "Scan All"
+    assert len(SCAN_BUTTONS) == 5  # 4 TFs + "Scan All"
     for btn in SCAN_BUTTONS:
         assert btn["cb"] in SCAN_LOOKUP
         assert "symbol" in btn