feat: date-range picker on the station history panel; drop PostgreSQL naming

/measurements/history/{code} accepts optional start/end date params that
override the hours window (end date inclusive). The dashboard history
card gains from/to date inputs beside the quick-range dropdown —
explicit dates win, changing the dropdown clears them. All user-facing
'PostgreSQL history' labels renamed to 'Station history'.

tests/test_dashboard.py

@@ -51,9 +51,13 @@ def test_dashboard_shows_hii_rainfall_layer():
     assert "Extreme > 150" in html
 
 
-def test_dashboard_loads_postgresql_history_chart():
+def test_dashboard_loads_station_history_chart():
     html = DASHBOARD_PATH.read_text(encoding="utf-8")
 
-    assert "PostgreSQL history" in html
+    assert "Station history" in html
+    assert "PostgreSQL" not in html
     assert "/measurements/history/" in html
     assert "history-chart" in html
+    # Date-range picker alongside the quick-range dropdown
+    assert 'id="history-start"' in html
+    assert 'id="history-end"' in html