feat(schedule): add course table screens and navigation

Add complete schedule functionality including:
- Schedule screen with weekly course table view
- Course detail screen with transparent modal presentation
- New ScheduleStack navigator integrated into main tab bar
- Schedule service for API interactions
- Type definitions for course entities

Also includes bug fixes for group invite/request handlers
to include required groupId parameter.

internal/dto/schedule_converter.go

@@ -0,0 +1,35 @@
+package dto
+
+import (
+	"encoding/json"
+
+	"carrot_bbs/internal/model"
+)
+
+func ConvertScheduleCourseToResponse(course *model.ScheduleCourse, weeks []int) *ScheduleCourseResponse {
+	if course == nil {
+		return nil
+	}
+	return &ScheduleCourseResponse{
+		ID:           course.ID,
+		Name:         course.Name,
+		Teacher:      course.Teacher,
+		Location:     course.Location,
+		DayOfWeek:    course.DayOfWeek,
+		StartSection: course.StartSection,
+		EndSection:   course.EndSection,
+		Weeks:        weeks,
+		Color:        course.Color,
+	}
+}
+
+func ParseWeeksJSON(raw string) []int {
+	if raw == "" {
+		return []int{}
+	}
+	var weeks []int
+	if err := json.Unmarshal([]byte(raw), &weeks); err != nil {
+		return []int{}
+	}
+	return weeks
+}