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_dto.go

@@ -0,0 +1,13 @@
+package dto
+
+type ScheduleCourseResponse struct {
+	ID           string `json:"id"`
+	Name         string `json:"name"`
+	Teacher      string `json:"teacher,omitempty"`
+	Location     string `json:"location,omitempty"`
+	DayOfWeek    int    `json:"day_of_week"`
+	StartSection int    `json:"start_section"`
+	EndSection   int    `json:"end_section"`
+	Weeks        []int  `json:"weeks"`
+	Color        string `json:"color,omitempty"`
+}