feat: add support for one-off recording schedules with start and end datetime

backend/models.py

@@ -321,9 +321,10 @@ class RecurringSchedule(Base):
     """
     Recurring schedule definitions for automated sound monitoring.
 
-    Supports two schedule types:
+    Supports three schedule types:
     - "weekly_calendar": Select specific days with start/end times (e.g., Mon/Wed/Fri 7pm-7am)
     - "simple_interval": For 24/7 monitoring with daily stop/download/restart cycles
+    - "one_off": Single recording session with specific start and end date/time
     """
     __tablename__ = "recurring_schedules"
 
@@ -333,7 +334,7 @@ class RecurringSchedule(Base):
     unit_id = Column(String, nullable=True, index=True)  # FK to RosterUnit.id (optional, can use assignment)
 
     name = Column(String, nullable=False)  # "Weeknight Monitoring", "24/7 Continuous"
-    schedule_type = Column(String, nullable=False)  # "weekly_calendar" | "simple_interval"
+    schedule_type = Column(String, nullable=False)  # "weekly_calendar" | "simple_interval" | "one_off"
     device_type = Column(String, nullable=False)  # "slm" | "seismograph"
 
     # Weekly Calendar fields (schedule_type = "weekly_calendar")
@@ -349,7 +350,11 @@ class RecurringSchedule(Base):
     cycle_time = Column(String, nullable=True)  # "00:00" - time to run stop/download/restart
     include_download = Column(Boolean, default=True)  # Download data before restart
 
-    # Automation options (applies to both schedule types)
+    # One-Off fields (schedule_type = "one_off")
+    start_datetime = Column(DateTime, nullable=True)  # Exact start date+time (stored as UTC)
+    end_datetime = Column(DateTime, nullable=True)    # Exact end date+time (stored as UTC)
+
+    # Automation options (applies to all schedule types)
     auto_increment_index = Column(Boolean, default=True)  # Auto-increment store/index number before start
     # When True: prevents "overwrite data?" prompts by using a new index each time