Fix schedule management and update documentation for database-backed configs

This commit addresses multiple issues with schedule management and updates
  documentation to reflect the transition from YAML-based to database-backed
  configuration system.

  **Documentation Updates:**
  - Update DEPLOYMENT.md to remove all references to YAML config files
  - Document that all configurations are now stored in SQLite database
  - Update API examples to use config IDs instead of YAML filenames
  - Remove configs directory from backup/restore procedures
  - Update volume management section to reflect database-only storage

  **Cron Expression Handling:**
  - Add comprehensive documentation for APScheduler cron format conversion
  - Document that from_crontab() accepts standard format (Sunday=0) and converts automatically
  - Add validate_cron_expression() helper method with detailed error messages
  - Include helpful hints for day-of-week field errors in validation
  - Fix all deprecated datetime.utcnow() calls, replace with datetime.now(timezone.utc)

  **Timezone-Aware DateTime Fixes:**
  - Fix "can't subtract offset-naive and offset-aware datetimes" error
  - Add timezone awareness to croniter.get_next() return values
  - Make _get_relative_time() defensive to handle both naive and aware datetimes
  - Ensure all datetime comparisons use timezone-aware objects

  **Schedule Edit UI Fixes:**
  - Fix JavaScript error "Cannot set properties of null (setting 'value')"
  - Change reference from non-existent 'config-id' to correct 'config-file' element
  - Add config_name field to schedule API responses for better UX
  - Eagerly load Schedule.config relationship using joinedload()
  - Fix AttributeError: use schedule.config.title instead of .name
  - Display config title and ID in schedule edit form

  **Technical Details:**
  - app/web/services/schedule_service.py: 6 datetime.utcnow() fixes, validation enhancements
  - app/web/services/scheduler_service.py: Documentation, validation, timezone fixes
  - app/web/templates/schedule_edit.html: JavaScript element reference fix
  - docs/DEPLOYMENT.md: Complete rewrite of config management sections

  Fixes scheduling for Sunday at midnight (cron: 0 0 * * 0)
  Fixes schedule edit page JavaScript errors
  Improves user experience with config title display

app/web/services/scheduler_service.py

@@ -149,6 +149,51 @@ class SchedulerService:
         except Exception as e:
             logger.error(f"Error loading schedules on startup: {str(e)}", exc_info=True)
 
+    @staticmethod
+    def validate_cron_expression(cron_expression: str) -> tuple[bool, str]:
+        """
+        Validate a cron expression and provide helpful feedback.
+
+        Args:
+            cron_expression: Cron expression to validate
+
+        Returns:
+            Tuple of (is_valid: bool, message: str)
+            - If valid: (True, "Valid cron expression")
+            - If invalid: (False, "Error message with details")
+
+        Note:
+            Standard crontab format: minute hour day month day_of_week
+            Day of week: 0=Sunday, 1=Monday, ..., 6=Saturday (or 7=Sunday)
+        """
+        from apscheduler.triggers.cron import CronTrigger
+
+        try:
+            # Try to parse the expression
+            trigger = CronTrigger.from_crontab(cron_expression)
+
+            # Validate basic format (5 fields)
+            fields = cron_expression.split()
+            if len(fields) != 5:
+                return False, f"Cron expression must have 5 fields (minute hour day month day_of_week), got {len(fields)}"
+
+            return True, "Valid cron expression"
+
+        except (ValueError, KeyError) as e:
+            error_msg = str(e)
+
+            # Provide helpful hints for common errors
+            if "day_of_week" in error_msg.lower() or (len(cron_expression.split()) >= 5):
+                # Check if day_of_week field might be using APScheduler format by mistake
+                fields = cron_expression.split()
+                if len(fields) == 5:
+                    dow_field = fields[4]
+                    if dow_field.isdigit() and int(dow_field) >= 0:
+                        hint = "\nNote: Use standard crontab format where 0=Sunday, 1=Monday, ..., 6=Saturday"
+                        return False, f"Invalid cron expression: {error_msg}{hint}"
+
+            return False, f"Invalid cron expression: {error_msg}"
+
     def queue_scan(self, scan_id: int, config_id: int) -> str:
         """
         Queue a scan for immediate background execution.
@@ -188,6 +233,10 @@ class SchedulerService:
             schedule_id: Database ID of the schedule
             config_id: Database config ID
             cron_expression: Cron expression (e.g., "0 2 * * *" for 2am daily)
+                           IMPORTANT: Use standard crontab format where:
+                           - Day of week: 0 = Sunday, 1 = Monday, ..., 6 = Saturday
+                           - APScheduler automatically converts to its internal format
+                           - from_crontab() handles the conversion properly
 
         Returns:
             Job ID from APScheduler
@@ -195,18 +244,29 @@ class SchedulerService:
         Raises:
             RuntimeError: If scheduler not initialized
             ValueError: If cron expression is invalid
+
+        Note:
+            APScheduler internally uses Monday=0, but from_crontab() accepts
+            standard crontab format (Sunday=0) and converts it automatically.
         """
         if not self.scheduler:
             raise RuntimeError("Scheduler not initialized. Call init_scheduler() first.")
 
         from apscheduler.triggers.cron import CronTrigger
 
+        # Validate cron expression first to provide helpful error messages
+        is_valid, message = self.validate_cron_expression(cron_expression)
+        if not is_valid:
+            raise ValueError(message)
+
         # Create cron trigger from expression using local timezone
-        # This allows users to specify times in their local timezone
+        # from_crontab() parses standard crontab format (Sunday=0)
+        # and converts to APScheduler's internal format (Monday=0) automatically
         try:
             trigger = CronTrigger.from_crontab(cron_expression)
             # timezone defaults to local system timezone
         except (ValueError, KeyError) as e:
+            # This should not happen due to validation above, but catch anyway
             raise ValueError(f"Invalid cron expression '{cron_expression}': {str(e)}")
 
         # Add cron job
@@ -294,11 +354,16 @@ class SchedulerService:
 
                 # Update schedule's last_run and next_run
                 from croniter import croniter
-                next_run = croniter(schedule['cron_expression'], datetime.utcnow()).get_next(datetime)
+                now_utc = datetime.now(timezone.utc)
+                next_run = croniter(schedule['cron_expression'], now_utc).get_next(datetime)
+
+                # croniter returns naive datetime, add UTC timezone
+                if next_run.tzinfo is None:
+                    next_run = next_run.replace(tzinfo=timezone.utc)
 
                 schedule_service.update_run_times(
                     schedule_id=schedule_id,
-                    last_run=datetime.utcnow(),
+                    last_run=now_utc,
                     next_run=next_run
                 )