Phase 2: Add config support for week_start_day and default_due_time

- Add WeekStartDay and DefaultDueTime fields to Config struct
- Set defaults: week_start_day=monday, default_due_time=empty
- Add GetWeekStart() and GetDefaultDueTime() helper methods
- Update ParseDate() to use configured week start day
- All tests passing

opal-task/internal/engine/config.go

@@ -4,14 +4,18 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
+	"time"
 
 	"github.com/spf13/viper"
 )
 
 type Config struct {
-	DefaultFilter string `mapstructure:"default_filter"`
-	DefaultSort   string `mapstructure:"default_sort"`
-	ColorOutput   bool   `mapstructure:"color_output"`
+	DefaultFilter  string `mapstructure:"default_filter"`
+	DefaultSort    string `mapstructure:"default_sort"`
+	ColorOutput    bool   `mapstructure:"color_output"`
+	WeekStartDay   string `mapstructure:"week_start_day"`
+	DefaultDueTime string `mapstructure:"default_due_time"`
 }
 
 var globalConfig *Config
@@ -72,6 +76,8 @@ func LoadConfig() (*Config, error) {
 	v.SetDefault("default_filter", "status:pending")
 	v.SetDefault("default_sort", "due,priority")
 	v.SetDefault("color_output", true)
+	v.SetDefault("week_start_day", "monday")
+	v.SetDefault("default_due_time", "")
 
 	// Try to read existing config
 	err = v.ReadInConfig()
@@ -110,6 +116,8 @@ func SaveConfig(cfg *Config) error {
 	v.Set("default_filter", cfg.DefaultFilter)
 	v.Set("default_sort", cfg.DefaultSort)
 	v.Set("color_output", cfg.ColorOutput)
+	v.Set("week_start_day", cfg.WeekStartDay)
+	v.Set("default_due_time", cfg.DefaultDueTime)
 
 	return v.WriteConfig()
 }
@@ -121,3 +129,16 @@ func GetConfig() (*Config, error) {
 	}
 	return LoadConfig()
 }
+
+// GetWeekStart returns the configured week start day
+func (c *Config) GetWeekStart() time.Weekday {
+	if strings.ToLower(c.WeekStartDay) == "sunday" {
+		return time.Sunday
+	}
+	return time.Monday // default
+}
+
+// GetDefaultDueTime returns the configured default due time (HH:MM format or empty)
+func (c *Config) GetDefaultDueTime() string {
+	return c.DefaultDueTime
+}