Add support for daily, weekly, monthly, yearly recurrence patterns

Previously, only numeric forms (1d, 1w, 1m, 1y) and plural word forms
(days, weeks, months, years) were supported for recurrence patterns.
The common adverbial forms (daily, weekly, monthly, yearly) would fail
with 'invalid recurrence pattern' error.

Now users can use natural language recurrence patterns:
- recur:daily   -> 1 day interval
- recur:weekly  -> 7 day interval
- recur:monthly -> 30 day interval
- recur:yearly  -> 365 day interval

Added test coverage for all four new patterns.

opal-task/internal/engine/recurrence.go

@@ -11,6 +11,7 @@ import (
 // ParseRecurrencePattern converts duration strings to time.Duration
 // Supports: 1d, 2w, 3m, 1y, 5min, 5hrs, 30sec
 // Also supports: days, weeks, months, years, minutes, hours, seconds
+// And common forms: daily, weekly, monthly, yearly
 func ParseRecurrencePattern(pattern string) (time.Duration, error) {
 	if len(pattern) == 0 {
 		return 0, fmt.Errorf("empty duration pattern")
@@ -21,10 +22,10 @@ func ParseRecurrencePattern(pattern string) (time.Duration, error) {
 		"second": time.Second, "seconds": time.Second, "sec": time.Second,
 		"minute": time.Minute, "minutes": time.Minute, "min": time.Minute,
 		"hour": time.Hour, "hours": time.Hour, "hrs": time.Hour, "hr": time.Hour,
-		"day": 24 * time.Hour, "days": 24 * time.Hour,
-		"week": 7 * 24 * time.Hour, "weeks": 7 * 24 * time.Hour,
-		"month": 30 * 24 * time.Hour, "months": 30 * 24 * time.Hour,
-		"year": 365 * 24 * time.Hour, "years": 365 * 24 * time.Hour,
+		"day": 24 * time.Hour, "days": 24 * time.Hour, "daily": 24 * time.Hour,
+		"week": 7 * 24 * time.Hour, "weeks": 7 * 24 * time.Hour, "weekly": 7 * 24 * time.Hour,
+		"month": 30 * 24 * time.Hour, "months": 30 * 24 * time.Hour, "monthly": 30 * 24 * time.Hour,
+		"year": 365 * 24 * time.Hour, "years": 365 * 24 * time.Hour, "yearly": 365 * 24 * time.Hour,
 	}
 
 	if duration, ok := wordDurations[pattern]; ok {

opal-task/internal/engine/recurrence_test.go

@@ -18,6 +18,11 @@ func TestParseRecurrencePattern(t *testing.T) {
 		{"2w", 14 * 24 * time.Hour},
 		{"1m", 30 * 24 * time.Hour},
 		{"1y", 365 * 24 * time.Hour},
+		// Test word forms
+		{"daily", 24 * time.Hour},
+		{"weekly", 7 * 24 * time.Hour},
+		{"monthly", 30 * 24 * time.Hour},
+		{"yearly", 365 * 24 * time.Hour},
 	}
 
 	for _, tt := range tests {