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/handler/schedule_handler.go

@@ -0,0 +1,140 @@
+package handler
+
+import (
+	"strconv"
+
+	"github.com/gin-gonic/gin"
+
+	"carrot_bbs/internal/pkg/response"
+	"carrot_bbs/internal/service"
+)
+
+type ScheduleHandler struct {
+	scheduleService service.ScheduleService
+}
+
+func NewScheduleHandler(scheduleService service.ScheduleService) *ScheduleHandler {
+	return &ScheduleHandler{scheduleService: scheduleService}
+}
+
+type createScheduleCourseRequest struct {
+	Name         string `json:"name" binding:"required"`
+	Teacher      string `json:"teacher"`
+	Location     string `json:"location"`
+	DayOfWeek    int    `json:"day_of_week" binding:"required"`
+	StartSection int    `json:"start_section" binding:"required"`
+	EndSection   int    `json:"end_section" binding:"required"`
+	Weeks        []int  `json:"weeks" binding:"required,min=1"`
+	Color        string `json:"color"`
+}
+
+type updateScheduleCourseRequest = createScheduleCourseRequest
+
+func (h *ScheduleHandler) ListCourses(c *gin.Context) {
+	userID := c.GetString("user_id")
+	if userID == "" {
+		response.Unauthorized(c, "")
+		return
+	}
+
+	week := 0
+	if rawWeek := c.Query("week"); rawWeek != "" {
+		parsed, err := strconv.Atoi(rawWeek)
+		if err != nil {
+			response.BadRequest(c, "invalid week")
+			return
+		}
+		week = parsed
+	}
+
+	list, err := h.scheduleService.ListCourses(userID, week)
+	if err != nil {
+		response.HandleError(c, err, "failed to list schedule courses")
+		return
+	}
+	response.Success(c, gin.H{"list": list})
+}
+
+func (h *ScheduleHandler) CreateCourse(c *gin.Context) {
+	userID := c.GetString("user_id")
+	if userID == "" {
+		response.Unauthorized(c, "")
+		return
+	}
+
+	var req createScheduleCourseRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		response.BadRequest(c, err.Error())
+		return
+	}
+
+	created, err := h.scheduleService.CreateCourse(userID, service.CreateScheduleCourseInput{
+		Name:         req.Name,
+		Teacher:      req.Teacher,
+		Location:     req.Location,
+		DayOfWeek:    req.DayOfWeek,
+		StartSection: req.StartSection,
+		EndSection:   req.EndSection,
+		Weeks:        req.Weeks,
+		Color:        req.Color,
+	})
+	if err != nil {
+		response.HandleError(c, err, "failed to create schedule course")
+		return
+	}
+	response.SuccessWithMessage(c, "course created", gin.H{"course": created})
+}
+
+func (h *ScheduleHandler) UpdateCourse(c *gin.Context) {
+	userID := c.GetString("user_id")
+	if userID == "" {
+		response.Unauthorized(c, "")
+		return
+	}
+	courseID := c.Param("id")
+	if courseID == "" {
+		response.BadRequest(c, "invalid course id")
+		return
+	}
+
+	var req updateScheduleCourseRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		response.BadRequest(c, err.Error())
+		return
+	}
+
+	updated, err := h.scheduleService.UpdateCourse(userID, courseID, service.CreateScheduleCourseInput{
+		Name:         req.Name,
+		Teacher:      req.Teacher,
+		Location:     req.Location,
+		DayOfWeek:    req.DayOfWeek,
+		StartSection: req.StartSection,
+		EndSection:   req.EndSection,
+		Weeks:        req.Weeks,
+		Color:        req.Color,
+	})
+	if err != nil {
+		response.HandleError(c, err, "failed to update schedule course")
+		return
+	}
+	response.SuccessWithMessage(c, "course updated", gin.H{"course": updated})
+}
+
+func (h *ScheduleHandler) DeleteCourse(c *gin.Context) {
+	userID := c.GetString("user_id")
+	if userID == "" {
+		response.Unauthorized(c, "")
+		return
+	}
+	courseID := c.Param("id")
+	if courseID == "" {
+		response.BadRequest(c, "invalid course id")
+		return
+	}
+
+	if err := h.scheduleService.DeleteCourse(userID, courseID); err != nil {
+		response.HandleError(c, err, "failed to delete schedule course")
+		return
+	}
+	response.SuccessWithMessage(c, "course deleted", nil)
+}