refactor: deduplicate engine internals, replace bubble sorts, remove dead code

Extract shared code that was duplicated across functions:
- taskJSON struct (MarshalJSON/UnmarshalJSON) to package-level type
- scanTask(scanner) helper for GetTask/GetTasks (~70 identical lines)
- monthNames map for parseMonthName/parseDayAndMonth
- applyNonDateAttribute helper for Apply/ApplyToNew
- resolveDisplayID calls replace inline loops in FormatTaskListWithFormat

Replace O(n²) bubble sorts with sort.Slice in all four report sort
functions (sortByUrgency, NewestReport, NextReport, OldestReport).

Remove dead code: formatTimeWithColor (unused, also used time.Now()
instead of timeNow()), getCurrentTimestamp (unnecessary wrapper).

Remove ~20 comments that restated the next line of code.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

opal-task/internal/engine/modifier.go

@@ -92,7 +92,6 @@ func (m *Modifier) Apply(task *Task) error {
 	for _, key := range m.AttributeOrder {
 		valuePtr := m.SetAttributes[key]
 
-		// Handle date attributes with relative expression support
 		if dateKeys[key] {
 			if err := applyDateAttribute(key, valuePtr, task, resolvedDates); err != nil {
 				return err
@@ -100,30 +99,11 @@ func (m *Modifier) Apply(task *Task) error {
 			continue
 		}
 
-		// Handle non-date attributes
-		switch key {
-		case "priority":
-			if valuePtr == nil {
-				task.Priority = PriorityDefault
-			} else {
-				task.Priority = Priority(priorityStringToInt(*valuePtr))
-			}
-		case "project":
-			task.Project = valuePtr
-		case "recur":
-			if valuePtr == nil {
-				task.RecurrenceDuration = nil
-			} else {
-				duration, err := ParseRecurrencePattern(*valuePtr)
-				if err != nil {
-					return fmt.Errorf("invalid recurrence: %w", err)
-				}
-				task.RecurrenceDuration = &duration
-			}
+		if err := applyNonDateAttribute(key, valuePtr, task); err != nil {
+			return err
 		}
 	}
 
-	// Apply tag changes
 	for _, tag := range m.AddTags {
 		if err := task.AddTag(tag); err != nil {
 			return err
@@ -160,7 +140,6 @@ func (m *Modifier) ApplyToNew(task *Task) error {
 	for _, key := range m.AttributeOrder {
 		valuePtr := m.SetAttributes[key]
 
-		// Handle date attributes with relative expression support
 		if dateKeys[key] {
 			if err := applyDateAttribute(key, valuePtr, task, resolvedDates); err != nil {
 				return err
@@ -168,26 +147,8 @@ func (m *Modifier) ApplyToNew(task *Task) error {
 			continue
 		}
 
-		// Handle non-date attributes
-		switch key {
-		case "priority":
-			if valuePtr == nil {
-				task.Priority = PriorityDefault
-			} else {
-				task.Priority = Priority(priorityStringToInt(*valuePtr))
-			}
-		case "project":
-			task.Project = valuePtr
-		case "recur":
-			if valuePtr == nil {
-				task.RecurrenceDuration = nil
-			} else {
-				duration, err := ParseRecurrencePattern(*valuePtr)
-				if err != nil {
-					return fmt.Errorf("invalid recurrence: %w", err)
-				}
-				task.RecurrenceDuration = &duration
-			}
+		if err := applyNonDateAttribute(key, valuePtr, task); err != nil {
+			return err
 		}
 	}
 
@@ -195,6 +156,31 @@ func (m *Modifier) ApplyToNew(task *Task) error {
 	return nil
 }
 
+// applyNonDateAttribute applies a non-date attribute (priority, project, recur) to a task.
+func applyNonDateAttribute(key string, valuePtr *string, task *Task) error {
+	switch key {
+	case "priority":
+		if valuePtr == nil {
+			task.Priority = PriorityDefault
+		} else {
+			task.Priority = Priority(priorityStringToInt(*valuePtr))
+		}
+	case "project":
+		task.Project = valuePtr
+	case "recur":
+		if valuePtr == nil {
+			task.RecurrenceDuration = nil
+		} else {
+			duration, err := ParseRecurrencePattern(*valuePtr)
+			if err != nil {
+				return fmt.Errorf("invalid recurrence: %w", err)
+			}
+			task.RecurrenceDuration = &duration
+		}
+	}
+	return nil
+}
+
 // parseRelativeExpression checks if a string is a relative date expression
 // Returns: baseAttr, operator, offset, isRelative
 // Example: "due-1d" -> "due", "-", "1d", true