Implement date range handling for vacation and unavailable events

- Added helper functions to generate ISO 8601 formatted start and end times for calendar days.
- Introduced logic to merge consecutive vacation dates into a single record for improved data representation.
- Updated the duty schedule import process to utilize the new date handling functions for unavailable and vacation events.
- Enhanced integration tests to validate the correct handling of vacation periods and unavailable dates.
- Modified the web application to display formatted date ranges for vacation and unavailable events.

tests/test_import_duty_schedule_integration.py

@@ -140,16 +140,16 @@ def test_import_full_flow_parse_then_import(db_url):
 
 
 def test_import_event_types_unavailable_vacation(db_url):
-    """Import creates records with event_type duty, unavailable, vacation."""
+    """Import creates duty, unavailable (full day), vacation (periods). Unavailable: same-day 00:00–23:59. Three consecutive vacation days → one record."""
     result = DutyScheduleResult(
         start_date=date(2026, 2, 16),
-        end_date=date(2026, 2, 18),
+        end_date=date(2026, 2, 20),
         entries=[
             DutyScheduleEntry(
                 full_name="Mixed User",
                 duty_dates=[date(2026, 2, 16)],
                 unavailable_dates=[date(2026, 2, 17)],
-                vacation_dates=[date(2026, 2, 18)],
+                vacation_dates=[date(2026, 2, 18), date(2026, 2, 19), date(2026, 2, 20)],
             ),
         ],
     )
@@ -159,9 +159,48 @@ def test_import_event_types_unavailable_vacation(db_url):
 
     session = get_session(db_url)
     try:
-        duties = get_duties(session, "2026-02-16", "2026-02-19")
+        duties = get_duties(session, "2026-02-16", "2026-02-21")
     finally:
         session.close()
     assert len(duties) == 3
     types = {d[0].event_type for d in duties}
     assert types == {"duty", "unavailable", "vacation"}
+
+    by_type = {d[0].event_type: d[0] for d in duties}
+    unav = by_type["unavailable"]
+    assert unav.start_at == "2026-02-17T00:00:00Z"
+    assert unav.end_at == "2026-02-17T23:59:59Z"
+    vac = by_type["vacation"]
+    assert vac.start_at == "2026-02-18T00:00:00Z"
+    assert vac.end_at == "2026-02-20T23:59:59Z"
+
+
+def test_import_vacation_with_gap_two_periods(db_url):
+    """Vacation dates with a gap (17, 18, 20 Feb) → two records: 17–18 and 20."""
+    result = DutyScheduleResult(
+        start_date=date(2026, 2, 16),
+        end_date=date(2026, 2, 21),
+        entries=[
+            DutyScheduleEntry(
+                full_name="Vacation User",
+                duty_dates=[],
+                unavailable_dates=[],
+                vacation_dates=[date(2026, 2, 17), date(2026, 2, 18), date(2026, 2, 20)],
+            ),
+        ],
+    )
+    num_users, num_duty, num_unav, num_vac = _run_import(db_url, result, 6, 0)
+    assert num_users == 1
+    assert num_duty == 0 and num_unav == 0 and num_vac == 2
+
+    session = get_session(db_url)
+    try:
+        duties = get_duties(session, "2026-02-16", "2026-02-21")
+    finally:
+        session.close()
+    vacation_records = [d[0] for d in duties if d[0].event_type == "vacation"]
+    assert len(vacation_records) == 2
+    starts = sorted(r.start_at for r in vacation_records)
+    ends = sorted(r.end_at for r in vacation_records)
+    assert starts == ["2026-02-17T00:00:00Z", "2026-02-20T00:00:00Z"]
+    assert ends == ["2026-02-18T23:59:59Z", "2026-02-20T23:59:59Z"]